Contributions to the Knowledge of Lower Cretaceous Ammonites from Kopet-Dag

Preface. In the summer of 1914, the student M. N. Sarkisov and I carried out the geological field practice required of us in the Kopet-Dag range. Taking into account the funds available to us for the expedition and other incidental circumstances, we chose the part of the range best known and most accessible to us—namely, the district of the city of Ashkhabad, between the frontier posts of Gedivar and Chaek. Here, in addition to a number of small excursions, we made a complete section of the range—along the course of the Firyuzi-Su stream from its emergence onto the plain to the Firyuzi frontier post, turning near the latter toward Mount Chapan, the highest point of the range, and then crossing to the other side of this mountain into Persia in the direction of the village of Dzhiristan. The collection we brought back is of little interest from the petrographic point of view, since in the part of the range examined no igneous rocks were encountered, and the whole district is composed exclusively of marls. The paleontological part of the collection is richer and is represented by cephalopods, sea urchins, lamellibranchs, and, in part, gastropods and brachiopods; the places in the examined part of the range richest in historical material proved to be: Mount Merkhoy, where the main part of the urchins was found; Mount Geabyul-Dag near the Cossack post of Chuli, where almost all the ammonites were collected, with the exception of a few specimens originating from Mount Dzhafru; Mount Kuropatkina, with lamellibranchs; and Mount Chapan, with part of the urchins and lamellibranchs, as well as gastropods and brachiopods.

Prof. M. A. Usov proposed that we undertake, as a diploma thesis, the treatment of the paleontological material brought back, and this was done by us under his immediate supervision in 1915; in this work I dealt with the ammonites, which constitute the greater part of our paleontological collection.

On the Necessity of Measuring the Dimensions of Ammonites

In the present work I have attempted to apply a mathematical method to the study of ammonites. The insufficiency of a simple description of forms and of merely appending their illustrations consists in the following. Even in photographs taken of the shell in three perpendicular planes, many details remain unclear, while a photograph from one side is, of course, wholly inadequate. The description itself, in which it is impossible to dispense with such terms as “rather broad,” “not very flat,” “slightly curved,” etc., cannot be satisfactory, since all concepts and definitions connected with the qualifiers “rather,” “not very,” “more or less,” “slightly,” etc., are so individual and inconstant—not only among different authors of monographs, but even in one and the same person—that they often leave the reader at a loss as to how precisely the given definition is to be understood. Thus the mathematical method gives not only the diameter, width, height above the suture, and other elements of the shell expressed in numbers, but also serves as a criterion when comparing specimens regardless of their size, if the constants of the shell are calculated in the form of ratios of width to diameter, height above the suture to diameter, and so on. In the monographs that served as aids in my work, one may note the presence of a tendency toward the mathematical method. Thus, A. d’Orbigny gives one constant, D. Anthula three constants, and L. Karakazansky appends to the descriptions of individual species whole tables and only

for this reason neither Professor I. Sinzow nor C. Jacob found it necessary to calculate these constants, and Prof. I. Sinzow does not even give the dimensions of the umbilicus of the shell.

My attempt to find quite characteristic constants even for genera still remains only an attempt, for the collection that served as material for the work contains a very limited number of specimens of individual forms, and a rigorous mathematical analysis is a matter for the future. Nevertheless, when comparing, for example, two genera, Parahoplites and Acanthohoplites, by means of the ratio of the diameters of the umbilicus to the diameters of the shells, one can already assert that for the genus Parahoplites, as understood by Prof. I. Sinzow, this ratio is never greater than 0.30, and in most cases is smaller and reaches even 0.20, whereas the ratio in Acanthohoplites rises to 0.40 and does not fall below 0.30.

The collection that served me as material for the work consists essentially of ammonite nuclei, and all measurements and calculations refer only to nuclei. Measurements of the elements of the shell (nucleus) were made in one section and refer chiefly to the last whorl.

Further, in establishing the systematic position of ammonites it is often necessary to clarify whether one is dealing with an adult or a young form. This question is resolved only under the basic assumption, confirmed by representatives of the modern fauna, that each form of ammonites in its growth is limited by certain bounds, attaining in the adult state a definite number of shell whorls. With such an assumption, the problem posed may be approached in two ways: either by establishing the normal number of shell whorls in the adult form of a given genus, or by analyzing the ontogenetic development of ammonites. Thus, counting the number of whorls on the specimens of the genera Acanthohoplites and Parahoplites present in the collection, and also from the figures in D. Anthula 1), Prof. I. Sinzow 2), P. Kazansky 3), and others, I did not encounter, with the exception of one form in D. Anthula, specimens with a number of shell whorls greater than 4 1/2—usually 3–4 whorls—and I am inclined to think that 4 will be the normal number of whorls in adult shells of the above-mentioned genera. And thus, if the forms of each genus of ammonites are characterized in the adult state by a definite number of shell whorls, then from this—among other things—one may draw the conclusion that two specimens with the same number of whorls and close in general outline and sculpture, but differing substantially in size, belong to different species or, at least, varieties.

In clarifying the difference between adult and young forms, besides the number of whorls, one must also be guided by the character of the sculpture. Investigators of the order of construction of cephalopod chambered shells have established that the first whorls, around the embryonic chamber, with which the animal is connected only by the siphon, cannot develop, for they do not enter into the animal’s organism; moreover, owing to the slowness of accumulation of whorls in ammonites, ontogenetic development well repeats phylogenetic development and, so to speak, becomes fossilized on the first whorls. But the phylogenetic development of different natural groups of ammonites is expressed especially distinctly in the change of the sculpture of their shells. It follows from this that the young and adult forms of one and the same species

1) D. Anthula. On the Cretaceous fossils of the Caucasus.—Contributions to Palaeontology and Geology. Vol. XII, 1898–900.
2) J. Sinzow. Investigation of some ammonitids from the Lower Gault of Mangyshlak and the Caucasus.—Proceedings of the Imperial Mineralogical Society. St. Petersburg. Second series. 1917.
3) P. Kazansky. Description of a collection of cephalopods from Dagestan.—Proceedings of the Tomsk Technological Institute. Vol. 32, book 4. 1913.

cannot be identical in the sculpture of the last whorl. And if such identity is observed in shells of different size and—especially—of a different number of whorls, then it is more logical to assign such forms to different species. Developing the proposition stated above, we must acknowledge that, in establishing a species, it is necessary to distinguish the juvenile and adult parts of the last whorl of the shell, and that, as the criterion for determining the systematic position of a form, we shall take into account the sculpture only of the adult part of its last whorl. Failure to observe this condition may introduce confusion into determinations, which, indeed, is found in the relevant literature. Thus, in the work of D. Anthula cited above, the forms figured in figs. 2a and 3a of pl. X are given as specimens of Parahoplites aschiltaensis, one shell being 70 mm and the other 45 mm in diameter. D. Anthula supposes that the smaller specimen is a younger form of the given species. But the larger specimen has 3½ whorls, and the smaller one 3; furthermore, the adult part of the penultimate whorl of the larger specimen is identical with the adult part of the last whorl of the small specimen both in the number of intermediate ribs and in the character of the ribbing. And so, if one mentally adds the missing ½ whorl to the small specimen, then the juvenile part of its last whorl and the juvenile part of the last whorl of the larger specimen will differ greatly—not only in the number of intermediate ribs, but also in the tubercles, which are absent in the large specimen, while in the small form they are present and are very sharp. Thus it will hardly be correct to regard these forms as belonging to one variety or even species, although they are close to one another, since the penultimate whorl of the large specimen bears tubercles—a circumstance indicating that the individuals under consideration have a common ancestor. If D. Anthula had taken into account only the adult halves of the last whorls of the given forms, then, probably, he would have given them different specific names. It is interesting to note that, like D. Anthula, Prof. I. Sinzov and P. Kazansky also assign both tuberculate and smooth forms to the species aschiltaensis.

In the further description, when establishing the specific significance of ammonite forms, we shall take into account the size, the number of whorls, and the character of the sculpture on the corresponding whorls of the shells.

Descriptive Part.

Genus Acanthohoplites Sinzow 1907.

The ambiguity of the existing diagnosis of the genus Acanthohoplites, the most important one in the collection described, does not allow me to confine myself merely to references to the relevant literature, but compels me to give, in addition to a full analysis of the existing views, my own personal characterization of this genus.

The genus Acanthohoplites was established by Prof. I. Sinzov; as the central typical form of this genus Prof. I. Sinzov took Parahoplites aschiltaensis D. Anthula 1898, separating the group of this species into a distinct genus. On the basis of the form aschiltaensis, Prof. I. Sinzov gives the following characterization of the genus Acanthohoplites (pp. 478–481):

“Acanthohoplites aschiltaensis is the central form of this group. From it, on one side, depart forms in which the cross-section gradually decreases; on the other side—forms with a strongly compressed cross-section. In the extreme representatives of the latter group the tubercles on the main ribs disappear completely. The lateral parts of the cross-sections are weakly convex. The outer part is flat and only at the anterior end slightly convex, and this convexity increases with age. The walls of the umbilicus are gentle. On mo-

on young whorls the main ribs are covered with tubercles (sharp), which adjoin closely the lower part of the umbilical wall. From these tubercles the main ribs divide into two branches, but before the venter they give three branches. Between the main ribs there are intermediate ones. At the beginning of the last and at the end of the penultimate whorl, on the main ribs, two pairs of nodes are observed, as in Douvilleiceras Cornuelianum, but later they disappear and the branching of the main rib begins from the lower angle. On the second half of the last whorl, where paired nodes are absent, arcuate—outwardly convex—main ribs appear, which alternate with intermediate ribs. The latter run in the same direction and disappear in the lower third of the flank.“ ... As for the suture line, the author, in giving the description, does not provide a figure; he says that the difference of the genus Acanthohoplites distinguished by him from the genus Parahoplites consists chiefly in the lesser asymmetry of the first lateral lobe, considering as the second distinctive character the tubercles on the young whorls of the shell.

The characterization of the genus Acanthohoplites given above is, of course, insufficient, and this was immediately stated in subsequent monographs. Thus, P. Kazansky, denying the great asymmetry of the first lateral lobe in Parahoplites and declaring that the origin of the genus Parahoplites has not been clarified and that the connection of this genus with Acanthohoplites is doubtful, nevertheless considers it possible to retain the generic name given by Prof. I. Sinzow, without adducing any other distinctive characters of the genus. But the unsatisfactory nature of Prof. I. Sinzow’s characterization of the genus Acanthohoplites is the result not so much of the unclear origin of the genus Parahoplites as of the absence of indications of any individual features of the latter. And the uncertainty of the genus Parahoplites arose because D. Anthula, distinguishing in this genus the groups Parahoplites Melchioris and Parahoplites aschiltaensis, of which the latter group was later entirely assigned by Prof. I. Sinzow to the genus Acanthohoplites, says that the principal distinctive character between these groups should be considered the tubercles on the young whorls in Par. aschiltaensis, absent in Par. Melchioris, although he further notes that this principal character has no absolute significance; moreover, from D. Anthula’s figures, for example in fig. 1 of pl. XI (X), it is evident that tubercles are not obligatory even on the young whorls of Par. aschiltaensis itself.

Thus the genus Parahoplites apparently ought to be defined by the character of the suture line. D. Anthula has an exact description of this line, but from the meaning of the text it is clear that D. Anthula, in his description, had in view the line of the form Parahoplites aschiltaensis. And so, as soon as Prof. I. Sinzow assigned the non-tuberculate forms Par. aschiltaensis to the genus Acanthohoplites, the genus Parahoplites seemingly ceased to exist. Such a conclusion is not unexpected: for example, Charles Jacob¹) believes that the genus Parahoplites is conditional, and leaves the generic name Parahoplites only for the group Melchioris, while referring the group aschiltaensis to the genus Douvilleiceras.

The noted uncertainty in the diagnosis of the genera Parahoplites and Acanthohoplites compels me to give a clearer characterization of the group Parahoplites Melchioris, by comparison with which it will then be easy to establish also the genus Acanthohoplites, which is more important for us.

On plate XI (X), fig. 2, D. Anthula gives an image of a very typical form from the group Parahoplites Melchioris, namely Parahoplites

¹) Charles Jacob. Etude sur les ammonites de l’horizon stratigraphique du gisement de Clansayes.—Bulletin de la société géologique de France. Quatrième série, tome cinquième, 1905.

Sjögreni. In this specimen the suture line is clearly visible; I have reproduced it in an unfolded form in Fig. 1. If the indicated suture line is taken as typical for the genus Parahoplites, then the characterization of the latter by the suture line may be presented as follows: 1) in Parahoplites, on the lateral side there are three lobes and two saddles, not counting the external ones (lobes k, l, and m and saddles b and c); 2) in Parahoplites the external lobe lies almost at the same height as the first lateral lobe; 3) as for the considerable asymmetry of the first lateral lobe in Parahoplites, to which Prof. I. Sinzow points, this feature occurs only in some representatives of the genus.

The sculptural characterization of the genus Parahoplites, in my opinion, is expressed by the following 10 characters found in typical forms: 1) absence of tubercles, at least on the last whorls; 2) the ribs only in rare cases bear umbilical thickenings; 3) the ribs are always sickle-shapedly curved; 4) the ribbing is sharp and not dense; 5) the intermediate rib is always single or absent; 6) branching of the ribs does not occur; 7) the ribs, crossing the siphonal side, almost always bend forward; 9) on the siphonal side the ribs are never made flat, and therefore the cross-section is always rounded; 10) the umbilicus is always less than \(1/3\) of the shell diameter.

Now, if we look closely at the representatives of the group Par. aschiltaensis and at the forms of my collection of the same type, we shall see that the genus Acanthohoplites possesses many characters distinguishing it from the genus Parahoplites. In the suture line of Acanthohoplites, represented in unfolded form in Fig. 2, we find the following peculiarities: 1) in Acanthohoplites on the lateral side there is only one lobe (k) and one saddle (b), whereas in Parahoplites the number of suture elements is much greater; 2) in Acanthohoplites the external lobe always lies considerably higher than the lateral lobe, whereas in Parahoplites these elements are situated at approximately the same height; 3) finally, the first lateral lobe of Acanthohoplites is sufficiently symmetrical.

In contrast to Parahoplites, the shell of Acanthohoplites has the following morphological peculiarities: 1) presence of tubercles in the majority of forms; 2) the ribs always produce umbilical thickenings; 3) the ribs, crossing the siphonal side, almost always pass into a plane; 4) the ribs on that same side never make a forward bend; 5) the cross-section of the shell is almost always high; 6) the umbilicus is close to or greater than \(1/3\) of the shell diameter. Finally, for a complete characterization of the genus Acanthohoplites it is necessary to add another 4 such independent characters: 7) the number of intermediate ribs fluctuates from 1 to 6; 8) branching of the ribs is observed not infrequently; 9) the form of the ribs and the density of the ribbing vary greatly; 10) the shell is always more or less flat.

Thereafter, wishing to establish the difference and to give a characterization of the genera Acanthohoplites and Parahoplites by the above-mentioned mathematical method, I compiled the following tables. The material for these tables consisted of measurements made by me directly on fossils or on photographic images of them in various authors, or else the results of measurements given in existing monographs. To save space, I do not give in the tables the results of the measurements, but give the recalculated ratios of these measurements, or constants; moreover, insofar as the material permits, the following constants are indicated: 1) the ratio of the umbilicus diameter to the shell diameter; 2) the ratio of the height above the seam of the last whorl to the shell diameter; 3) the ratio of the height of the last whorl to the shell diameter; and 4) the ratio of the thickness of the last whorl to the shell diameter.

Table 1.

Parahoplites.

D. Anthula.

P. Kazansky.

Prof. I. Sintsov.

From these tables (1–2) the following conclusion may be drawn. The ratio of the diameter of the umbilicus to the diameter of the shell in Parahoplites lies within the limits from 0.20 to 0.30, reaching the latter limit in very rare cases, in most of which an error in measurement is possible. For the genus Acanthohoplites these limits are defined as 0.30—0.40; the latter limit is rare; sometimes, in transitional forms, there is also a lowering of the first boundary to 0.26. In general, however, the lowering of this constant in the genus Acanthohoplites occurs in most cases in small specimens, where an error in measuring the diameter of the umbilicus of 1 mm or 1/2 mm is quite possible and has enormous significance. Let us take, for example, the form Acanthohoplites sub-Tobleri, figured by P. Kazansky in fig. 51, pl. III. According to P. Kazansky’s measurements, this specimen, with a shell diameter of 17 mm, has an umbilicus diameter of 5 mm; according to my measurements, however, the umbilicus diameter is 6 mm. Hence P. Kazansky found the constant under consideration to be equal to \(5/17 \cong 0.29\); in reality it is closer to \(6/17 \cong 0.35\). I shall point out one more example from P. Kazansky’s material. In fig. 48, pl. III of his monograph, Acanthohoplites aplanatus Kasansk. is figured, for which the diameters of the umbilicus and of the shell are given respectively as 12 mm and 48 mm; according to

according to my measurements these quantities are closer to 16 mm and 51 mm. And here, according to P. Kazansky, the constant is considerably less than 0.30, while according to my measurements it is equal to 0.31. It should be noted that the error in measuring the elements is caused in part by the fact that one part of the fossil represents the nucleus, while the other has also preserved the shell wall. It goes without saying that, when measuring the diameters of the shell and the umbilicus, the appropriate corrections must in this case be made.

On the basis of all that has been set out, I venture to conclude that for transitional forms of the genus Acanthohoplites the ratio of the diameter of the umbilicus to the diameter of the shell should lie within the limits from 0.30 to 0.40; for the genus Parahoplites the same ratio fluctuates between 0.20–0.29. As for the other constants, they apparently cannot be used for distinguishing these two genera. For the genus Acanthohoplites in general we have the following limits of ratios: 1) height above the suture to the diameter of the shell from 0.35–0.51; 2) height of the last whorl to the diameter of the shell from 0.29–0.46; and 3) thickness of the last whorl to the diameter of the shell from 0.26–0.47.

In confirmation of I. Sinzow’s opinion that the genus Acanthohoplites gives two branches—one with whorls becoming thinner and the other with whorls becoming thicker—I can point out that in my material the forms of Acanthohoplites likewise divide into two groups with corresponding limits of the ratio of thickness to shell diameter of 0.26–0.33 and 0.33–0.44, and these groups also differ in some other morphological characters.

Table 2.

Acanthohoplites.

Stud. Danilovich.

II. Kazansky.

Pr. I. Sinzow.

1. Acanthohoplites aschiltaensis Anthula sp.

1. Parahoplites aschiltaensis. Anthula. p. 117, Pl. X Fig. 2—4.
2. Acanthohoplites aschiltaensis. Sinzow. Pl. V, Fig. 1—12; Pl. VI. Fig. 19—21.

1. Acanthohoplites aschiltaensis. I. Kazansky, p. 67;
   pl. III, fig. 47.

The three specimens available in the collection described differ in no essential respect, in their figures and description, from the forms indicated by the authors.

2. Acanthohoplites cf. multispinatus Anthula sp.

1. Parahoplites multispinatus. D. Anthula. Vol. XII, p. 119;
   Taf. X, Fig. 5a—c.

2. Acanthohoplites multispinatus. Sinzow. p. 492, Taf. VII, Fig. 1—8a.

The specimen present in the collection is very close, in description and figures, to the form of I. Sinzow, but since it is enclosed in the rock and almost cannot be separated from it, it is not possible to determine the species precisely.

3. Acanthohoplites multispinatus Anthula sp., aff. var. ternicostata Sinzow

1. Acanthohoplites multispinatus. Sinzow. p. 495, Taf. VII,
   Fig. 1—8a.

The three specimens available in the collection described are fairly close to the description and figures of Prof. I. Sinzow. All three differ in that they appear to lack both the siphonal and the lateral pairs of tubercles. Specimen No. 2 also differs in the number of intermediate ribs: thus, in I. Sinzow’s specimens the number of intermediate ribs varies from 1 to 2, whereas in my specimen the number of intermediate ribs is always two. Unfortunately, my specimens do not provide all the data for establishing a new species, but it seems to me that the variety ternicostata should be regarded as an independent species.

4. Acanthohoplites robusta Sinzow emend. Danilowitch.

1. Acanthohoplites multispinatus Anthula sp., var. robusta. Sinzow. P. 496; Pl. VII, figs. 4, 7 and 8.

My specimen is identical with the figure of the form Ac. multispinatus, var. robusta according to Sinzow and agrees with it in description, but I do not find it possible to regard this form as a variety of the species Acanthohoplites multispinatus Anthula sp., owing to the absence in it of both lateral and siphonal tubercles. A similar idea was also expressed by P. Kazansky when treating his material. On this basis I decide to separate the variety established by Sinzow into a distinct species, retaining for it the author’s name robusta.

5. Acanthohoplites multispinatus Anthula, var. raricostata n. var.

1. Parahoplites multispinatus. D. Anthula. Taf. X, Fig. 5a–c; S. 119.
2. Acanthohoplites multispinatus. Sinzow. S. 492; Taf. VII, Fig. 1–8a.
3. Acanthohoplites multispinatus. P. Kazansky. P. 80.

The umbilicus is wide, rather deep, with a rounded wall. The shell has rather rapidly increasing whorls of broadly trapezoidal form in transverse section. Up to 15 main ribs on a whorl; there is always one intermediate rib. The main ribs are very unequal: some have a ridge-like swelling on the umbilical part, others only a thickening and 2 pairs of tubercles on the lateral sides. On the thin part of the last whorl all the main ribs bear tubercles and have thickenings on the siphonal side. All ribs are slightly curved; on the siphonal side they are considerably weakened and differ in thickness depending on their order.

Convergence and difference. This specimen is closest to the figure and description of Parahoplites multispinatus D. Anthula, but differs from it in: 1) a number of ribs half as great; 2) the number of intermediate ribs; 3) the absence of a siphonal pair of tubercles on both the main and the intermediate ribs; 4) the different thickness of the main and intermediate ribs. On the basis of these distinctions I consider it possible to regard my specimen as var. raricostatus n. var.

6. Acanthohoplites cf. Bigoti Seunes sp.

1. Acanthoceras Bigoti. Seunes. Notes quelques Ammonites du Gault.—Bulletin de la Soc. geolog. de France. 3-me serie. Tome XV; p. 566; pl. XIV; fig. 3—4.

2. Acanthohoplites Bigoti. Sinzow. p. 502; Taf. IV, fig. 18—20.

My specimen is close to the figure of Prof. Sinzow, but is very poorly preserved and therefore difficult to determine.

7. Acanthohoplites subangulicostatus Kasansk.

1. Acanthohoplites subangulicostatus. P. Kasansky. pp. 83; pl. IV, figs. 16—17.

My specimen is close to the specimens in P. Kasansky’s collections, differing only in its somewhat smaller umbilicus.

8. Acanthohoplites aff. Trautscholdi Sim, Sorok. et Bazew.

1. Ammonites Trautscholdi. Simonovitsch, Sorokin und Bazewitsch.—Materialien zur Geologie des Kaukasus. S. 100, Taf. V, Fig. 2a and b.

2. Acanthoceras Migneni. Seunes. Bulletin de la soc. geolog. de France. 3-me serie. T. XV; p. 569; pl. XII fig. 3a et 6.

1. Acanthohoplites Trautscholdi. Sinzow. P. 499. Pl. IV, Figs. 9–17.

My specimen corresponds well to figures 9 and 16 and to Prof. Sinzow’s description. The latter considers the smaller form to be more slender than the large one, with which I find it possible to disagree on the grounds that, as I indicated in the introduction, the number of whorls in the larger and smaller specimens is almost the same. And it seems to me that my specimens nos. 25, 35, and the specimen of Prof. Sinzow almost identical with them according to figure no. 9 should be separated as an independent species; however, I do not venture to do this because of the insufficiency of the material.

9. Acanthohoplites Abichi Anthula sp.

1. Parahoplites Abichi. Anthula. Pl. (VIII) IX, Fig. 2a–b.
2. Acanthohoplites Abichi. Sinzow. P. 490, pl. VI, figs. 1–3.

Shell diameter = 32 mm and diameter of umbilicus 11 mm; D—umbilicus / D—shell = 0.35.

The single specimen present in the collection described here is almost identical in description and figures with Anthula’s form. As for the Acanthohoplites Abichi figured by Prof. Sinzow, it must be noted that they have only a very remote resemblance both to Anthula’s figures and to my specimen.

10. Acanthohoplites Uhligi Anthula sp.

1. Parahoplites Uhligi. Anthula. Pl. Fig. 1a–b; p. 114.
2. Acanthohoplites Uhligi. N. Karakasch. P. 86; pl. V, figs. 71–72.

My specimen is slightly compressed, but very close to Anthula’s figure and identical with the latter’s description.

11. Acanthohoplites aff. Anthulai Kasansk.

1. Acanthohoplites Anthulai. Kazansky. P. 84; pl. IV, fig. 68; pl. V, fig. 69.

A small shell with high and broad whorls. The umbilicus is wide, shallow, with a rounded wall. The sculpture consists of ribs. There are 15 main ribs on a whorl. There are from 1 to 2 intermediate ribs on the adult part of the last whorl, and more on the young part. The main ribs are swollen at the umbilicus, thin in the middle, thickened and slightly bent on the siphonal side. If a main rib branches, a tubercle is noticeable at the point of branching. The strength of the main ribs is very uneven.

This specimen comes closest to Acanthohoplites Anthulai Kazansky, differing in the smaller number of intermediate ribs, the branching of the main ribs, and the presence of tubercles; moreover, the cross-section can only with difficulty be taken as a trapezium. But the dimensions and the ratio of the umbilicus to the diameter coincide with Kazansky’s data for Ac. Anthulai, on the basis of which I consider my form related to the species Anthulai.

12. Acanthohoplites cf. Sinzowi Kasansk.

1. Acanthohoplites Sinzowi. Kazansky. Pl. III, figs. 52—55.

A fragment of a shell, in the character of its ribbing and in cross-section, is almost identical with the specimens of the collections of P. Kazansky, differing only in somewhat larger dimensions.

13. Acanthohoplites Ferandianus d’Orbigny sp.

1. Ammonites Ferandianus. d’Orbigny. Paléontologie Française—Terrains crétacés I; p. 324; pl. 96; figs. 4—5.

2. Parahoplites Ferandianus. D. Anthula. S. 110.

Specimen No. 11 is poorly preserved, strongly weathered, and therefore, it may be that its constant—the ratio of the umbilicus to the diameter of the shell—gives a value of 0.28, whereas in the better-preserved specimen it is 0.33. Both specimens are very close to d’Orbigny’s figure and ratio.

14. Acanthohoplites quadratus Kasansk.

1. Acanthohoplites quadratus. P. Kasansky. P. 78; pl. IV, fig. 64.

The two specimens in my collection are almost identical with the specimens of P. Kasansky, both in the figures and in the description. The constants of the specimen with a diameter of 22 mm agree almost exactly with Kasansky’s data. The specimen with a diameter of 27 mm gives the same constant as in Kasansky, except for the ratio of the umbilicus to the diameter, differing, however, by an insignificant amount.

15. Acanthohoplites Nolani Seunes sp.

1. Hoplites Nolani. Charles Jacob. Gisement de Clansayes.—Bulletin de la soc. géol. de France, 4-me série. Tome 5; p. 408.
2. Acanthohoplites Nolani. Sinzow. P. 503; pl. VIII, figs. 1—13.

My two specimens are of the original species Acanthohoplites Nolani Seunes, of which one is complete and the other is a fragment, very close to Sinzow’s description and figures. But I consider it my duty to point out that, in my opinion, the species Nolani, as understood by Sinzow, is too ...

is extensive, since Sinzov assigns to this species, not even as varieties, specimens whose diameters differ by 100 mm or more. These specimens do not represent adult and juvenile forms of one and the same species, since the number of whorls in such specimens is either the same or differs by 1/2 whorl. Moreover, Prof. Sinzov does not always indicate that the smaller form is considered by him to be juvenile. The composite character of this species is already evident from the fact that from eight specimens Prof. Sinzov distinguished three varieties of the species. Having insufficient material for the precise separation of the species Nolani, I follow the authority of Prof. Sinzov and, among the 5 forms remaining in my collection that approximate this species, distinguish the following three varieties.

16. Acanthohoplites Nolani Seunes, var. pygmaea Sinzow.

My specimen is almost identical with the figure and description in Prof. Sinzov, but has a smaller diameter and, correspondingly, a smaller number of whorls, representing only the large form.

17. Acanthohoplites Nolani Seunes, var. subrectangulata Sinzow.

My specimen is rather strongly crushed, and therefore does not allow the results of measurement to be given, but in general appearance, the character of the ribbing, and other features it fully corresponds to the description and figures of Prof. Sinzov.

18. Acanthohoplites Nolani Seunes, var. crassa Sinzow.

My specimen is very similar to the figures and identical according to the description of Prof. I. Sinzov.

1. Acanthohoplites variicostatus n. sp.

A small shell with rapidly growing, high and thick whorls. The umbilicus is broad, shallow, with rather steep walls. Sculpture—ribs of 3 orders. Ribs of the 1st order (main ribs) number 6–7 on a whorl; these ribs are thick, sharply expressed, bear swellings at the umbilicus, are ornamented with tubercles: a pair on the siphonal part and one each on the lateral sides. On younger whorls the ribs of the 1st order differ from the ribs of the 2nd order. The latter number up to 20 on a whorl, from 3 to 5 between the main ribs. Ribs of the 3rd order are more often branches of ribs of the 1st and 2nd orders and more rarely are independent intermediate ribs, always in the number of one rib. Ribs of the 2nd and 3rd orders are thin, smooth, but clearly expressed. On the siphonal side the 2nd and 3rd orders of ribs are not distinguishable from one another. All ribs are sickle-shapedly curved.

Similarities and differences. The described specimen bears many features characteristic of the collective group Acanthohoplites Nolani Sinzow, but differs in the presence of 3 orders of ribs and tubercles on the ribs of the 1st order, approaching in this character Acanthohoplites multispinatus Anthula, but differing from that species by an incomparably smaller number of main ribs and a much larger number of intermediate ones. On the basis of these differences and the presence of purely individual ribs of the 3rd order, I find it possible to regard this species as n. sp.

1. Acanthohoplites archari cornus n. sp.

Large shells with high and broad whorls of almost regular elliptical cross-section. The umbilicus is very broad, more than \(1/3\) of the shell diameter, fairly deep, with a rounded wall. The sculpture is expressed by ribs. The main ribs bend at the umbilicus and in this place bear a noticeable thickening; their number varies: specimen no. 8 bears 30, no. 9—33, and no. 10 even 40 main ribs. There is almost always one intermediate rib, very rarely two. No bifurcation of ribs is observed. The ribs, in comparison with the intermediate ones, are not thick, but are rather sharply expressed. On the siphonal side the main and intermediate ribs are indistinguishable from one another. The suture line (figs. 5, 6 and 7) belongs to the typical suture of Acanthohoplites aschiltaensis, but differs in the characteristically altered middle part of the first lateral lobe.

These forms are closest to the species Acanthohoplites Uhligi, but differ, in addition to the above-mentioned difference in the suture line, by the lesser curvature of the ribs, the smaller number of main ribs, the absence of their bifurcation, and the larger dimensions of the shell with the same number of whorls. On the basis of what has been said above, I consider it possible to distinguish these forms as an independent species, Acanthohoplites archaricornus n. sp.

21. Acanthohoplites sp.

The three fragments of large shells present in the collection undoubtedly belong to the genus Acanthohoplites, since on them the suture line, typical of Acanthohoplites aschiltaensis, is clearly visible.

It is not always possible to establish the specific significance of forms from fragments in general; the fragments I have possess certain features distinguishing them from all known representatives of the genus Acanthohoplites. Therefore, not venturing to establish new species from fragments alone, I leave them only the generic name Acanthohoplites sp.

Genus Parahoplites Anthula 1898.

22. Parahoplites Melchioris Anthula.

1. Parahoplites Melchioris. Anthula. S. 112; Taf. VIII (VII): Fig. 4a–e, 5a–в.

2. Parahoplites Melchioris. Sinzow. P. 458; pl. II, figs. 1–5.

3. Parahoplites Melchioris. Kazansky. P. 90; pl. V, figs. 76–78.

My two specimens, of which one is strongly weathered and the other is a small fragment, are so characteristic in their ribbing and so close to the specimens in P. Kazansky’s collection that they may without doubt be accepted as Parahoplites Melchioris Anthula.

Locality: Marz-Dzhafru Mountains.

23. Parahoplites versicostatus Michelin sp.

1. Ammonites versicostatus. Michelin. Mém de la Soc. géolog. de Fr. t. 3; p. 101; pl. XII, fig. 10.

2. Ammonites versicostatus. D’Orbigny. Paléontologie Française. Terains crétacés. I. p. 273; pl. 81, fig. 1–3.

1. Parahoplites versicostatus. Anthula. p. 110.

My specimen represents an exact copy of d’Orbigny’s figure and corresponds to the latter’s description. The specimen gives a constant for the ratio of umbilicus to diameter of 0.32, i.e., greater than is characteristic of the genus Parahoplites. This deviation can to a certain degree be explained by an error in measuring the given form, which is small in size, since if the umbilicus is taken not as 7, but as 6.5 mm, then the constant will already be 0.29, i.e., it will correspond to the genus Parahoplites.

Genus Hoplites Neumayr 1875.

24. Hoplites (Deshayesites) cf. Deshayesi Leymerie sp.

For the synonymy see P. Kazansky. p. 100.

Two small fragments of shells in my collection, with well-preserved ribbing, are completely identical with specimens of P. Kazansky’s collection.

Locality: Marz-Dzhafru Mountains.

25. Hoplites (Deshayesites) cf. Lavaschensis Kasansk.

1. Hoplites (Deshayesites) cf. Lavaschensis—P. Kazansky. p. 105; pl. VI, figs. 76–77.

The shell fragment in the collection is strongly compressed, but in the character of its ribbing it is very similar to a specimen of P. Kazansky’s collection.

Locality: Marz-Dzhafru Mountains.

Genus Desmoceras Zittel 1884.

26. Desmoceras aff. Saltense Kasansk.

1. Desmoceras Saltense. Kazansky. p. 110; pl. VII, figs. 94–95.

My specimen is very close to the specimens of the collection of P. Kazansky. The constants established for it scarcely differ from those obtained by me. Only because my specimen is flatter, its constant of the ratio of the thickness of the last whorl to the diameter of the shell is 0.36, whereas in Kazansky’s specimens it is =0.42–0.43. Growth lines and sickle-shaped furrows, of which Kazansky mentions, are present on my specimen, but are very poorly distinguishable.

27. Sonneratia sp.

There is a small fragment with high and rather thick whorls. The umbilicus is shallow, rather broad, with a rounded wall. The sculpture consists of ribs; the main ribs bear a slight thickening near the umbilicus. There is one intermediate rib, sometimes appearing as a branch of the main one. All ribs are sickle-shaped; on the siphonal side they are bent forward; here the main and intermediate ribs are indistinguishable from one another. In comparison with the intervals, the ribs are fairly thick. I do not find it possible, from this fragment, to determine the species, but I suppose that it belongs to the species Sonneratia tenuis Sinzow.

Locality: Mars–Jafru Mountains.

28. Lytoceras sp.

My specimen, enclosed in rock, represents a small shell with small and thick whorls. The umbilicus must have been broad, fairly deep, with a gently sloping wall. The shell is almost smooth—without sculpture; on the whorls it bears sickle-shaped furrows numbering 7, and perhaps more. On the basis of the available characters it is entirely impossible to determine the species.

Genus Douvilleiceras Grossouvre 1893.

Not considering it possible to follow the usual understanding of this genus, which was established by Jacob, who assigned to Douvilleiceras the whole group of Parahoplites aschiltaensis Athula, I adhere to the opinion of P. Kazansky, and can also note that the specimens of the genus Douvilleiceras present in my collection differ strongly from Parahoplites in sculpture and in the general form of the shell; as for the suture line, in the absence of the corresponding material I cannot make any statements on this matter.

29. Douvilleiceras cf. subnodoso-costatum Sinzow.

1. Douvilleiceras subnodoso-costatum. Sinzow. “Die Beschreibung einiger Douvilleiceras-Arten aus dem Oberen Neocom Russlands.” Proceedings of the St. Petersburg Mineralogical Society. 2nd series, vol. 44, issue 1, p. 175, pl. II, fig. 3.

The shell fragment in my collection is fairly close to Prof. Sinzow’s figure, but, owing to the small size of the fragment, which comprises about half a whorl, it is impossible to determine the species precisely.

30. Douvilleiceras cf. seminodosum Sinzow.

1. Douvilleiceras seminodosum. Sinzow. Douvilleiceras-Arten. p. 165; pl. I, figs. 3–6.

2. Douvilleiceras seminodosum. Kilian. Lethaea geognostica, p. 283.

3. Douvilleiceras seminodosum. Kazansky. p. 64; Plate III, figs. 42–43.

The specimen I have represents several young whorls of this form and differs in no way from the figures and description of Prof. Sinzow. In view of the poor preservation of the shell and its small size, I do not provide a plate.

31. Douvilleiceras magnum n. sp.

There is only one specimen of this genus. The transverse section of the shell is elliptical, and its whorls are low and thick.

The umbilicus is broad and deep, with steep walls. The sculpture of the last whorl is represented by coarse ribs and tubercles. There are up to 26 principal ribs on the last whorl, and these ribs bear two pairs of branching tubercles. The outer lateral pair of tubercles is more sharply expressed than the umbilical one, which, moreover, does not occur on every rib. Between the principal ribs of the last whorl there is only one intermediate rib each. Branching of the ribs is not observed here.

Because the shell has broken into pieces, it is possible to give a description also of its penultimate whorl. The transverse section of this whorl does not differ from that described and is characterized by the same constants.

The essential difference lies in the sculpture and in the number of ribs. There are up to 22 principal ribs here, and they always bear three pairs of tubercles, of which the siphonal pair is most sharply expressed, the first lateral pair more weakly, and the umbilical tubercles still more weakly. It is interesting to note that the siphonal tubercles, passing onto the more adult parts of the whorl, become weaker and on the young part of the last whorl pass into simple thickenings of the principal ribs, and then disappear entirely. Here there is likewise one intermediate rib each, but on the young part of this penultimate whorl it sometimes disappears. In general, the sculpture of this whorl is expressed more sharply than on the most adult part of the shell.

Similarities and differences. The representatives of Douvilleiceras in the collection I have studied come closest, in general, to the forms of P. Kazansky. But the greatest diameter of shells of Douvilleiceras in Kazansky’s collection, namely in Douvilleiceras Waageni, does not exceed 160 mm, whereas the diameter of my specimen is 270 mm; if, then, one compares the constants of my specimen with Kazansky’s data, presented in the following table, the closest species proves to be Douvilleiceras intermedium.

And according to the description this species is close to my specimen, but, unfortunately, P. Kazansky does not indicate the number of ribs on the whorl. In any case, there is a very substantial difference between the species being compared, consisting in the fact that the shell diameter of Douvilleiceras intermedium reaches only 35 mm. It is interesting to note that the penultimate whorl of my specimen differs rather sharply from its last whorl and resembles the last whorl of Douvilleiceras Martini, especially in the figure of d’Orbigny, differing only in its less sharply expressed tubercles. But since the tubercles in the juvenile part of the penultimate whorl of our specimen become sharper, it may be supposed that its first whorls will be still closer to Ammonites Martini, which may thus be regarded as the predecessor of the form newly established by me.

32. Douvilleiceras spinosum n. sp.

There is only one specimen of this species. The transverse section of the shell is elliptical, and its whorls are thick and low. The umbilicus is wide and deep, with a steep wall. The most characteristic elements are the tubercles, present in 3 pairs. The sharply expressed siphonal tubercles are connected with the gradually diminishing lateral tubercles by means of a rather well-projecting rib, and there are 18 such ribs on one whorl. Intermediate ribs are absent, and only on the juvenile part of the whorl does there appear one intermediate rib with a pair of siphonal tubercles. On the preceding whorls, covered by the subsequent ones, one can see umbilical tubercles and, up to half of them, tubercles of the lateral row. Its lobate line is also very close to the line of Ammonites Martini d’Orbigny, but differs from the figure given by d’Orbigny in the greater dissection of the secondary lobes of the saddles.

Similarities and differences. Both in its constants and in its somewhat original sculpture, this form does not quite fit within the limits of the known representatives of the genus Douvilleiceras. It comes closest to Douvilleiceras Martini, differing in lower whorls, the absence of an intermediate rib on the last whorl, and, as it were, in the more sharply expressed character of the tubercles.

A comparison of all the facts indicates that this form should nevertheless be assigned to the genus Douvilleiceras, representing a new species of it, which, because of the sharp character of its tubercles, I consider it possible to name spinosum.

33. Ammonites sp.

A small shell with slowly increasing broad and low whorls and with a wide, about \(1/3\) of the shell diameter, and deep umbilicus. The sculpture is very original. The shell is divided by 6–7 transverse rows of powerful tubercles, forming, as it were, ribs with three pairs of tubercles. The siphonal pair of tubercles is the strongest and sharpest; the first lateral pair is also strong, but smaller; the umbilical pair is expressed much more weakly than the preceding ones. Between these tuberculate ribs, which may be called the principal ribs, are intermediate ribs, smooth and thin.

Each pair of principal ribs encloses between them from 5 to 7 intermediate ones. The latter begin as an inconspicuous stroke on the rounded wall of the umbilicus and thicken toward the siphonal side, without producing tubercles. Sometimes an intermediate rib adjacent to a principal one appears as if it were its branch, originating from the second lateral tubercle of the principal rib.

Affinity and differences. The specimen described is so original that I do not venture to assign it to any of the known genera—all the more so since its suture line is unknown to me. I can only indicate that this specimen is closest, in the general character of the shell, to the genus Douvilleiceras, but differs from representatives of this genus by the exceptional strength of the tubercles and by the number of intermediate ribs, equal to 5–7, whereas Douvilleiceras have at most 3 intermediate ribs.

Conclusion.

From the table given below it is evident that all known species of the genus Acanthohoplites belong to the Aptian or to the lower Gault, which in essence is not a discrepancy. Thus the bed from which the ammonite specimens of the collection described were taken belongs to the Aptian stage. This conclusion is in agreement with the fact that, in the marls near the town of Merv, which constitute the underlying stratigraphic group, there are found forms of sea urchins Heteraster oblongus and Heteraster Couloni, which are considered to be of Neocomian age. Since all the material studied, with the exception of 5 specimens, was taken from a single bed, there is no doubt that the newly established ammonite species will characterize the same horizon; some of them are probably typical Aptian forms.

The geographical position of our deposits indicates that they belong to the equatorial province of the Mediterranean geosyncline. And indeed, of all the described forms, only Hoplites у Deshayesites Deshayesi, and even that found in a single specimen, is a form usual for the Cretaceous deposits of the temperate belt and which entered the sea of the Kopet-Dag region, perhaps, because of its cosmopolitan character. All the remaining ammonite species have so far been discovered chiefly in the deposits of neighboring regions: the Kopet-Dag, Mangyshlak, and the Caucasus. Since, on the other hand, among equatorial species enjoying a wider distribution one can point only to Acanthohoplites aschilaensis, found in Tunisia, Peru, Mexico, and France, it is natural to conclude that the Lower Cretaceous sea of the indicated Central Asian regions was somewhat enclosed, and that the greater part of the fauna contained in it must be regarded as indigenous.

Distribution of the described forms:

Fig. 2.

No. 17.

D. Anthula

Fig. 1.

(this line taken from the illustration)

Parahoplites Sjögreni, fig. 2, pl. XI

D. Anthula, fig. 3, pl. XI

Fig. 3.

(Parahoplites aschiltaensis)

Fig. 4.

(this line taken from the illustration)

Acanthohoplites Nolani, fig. 1, pl. VIII

Fig. 5.
No. 8.

Fig. 6.
No. 9.

Fig. 7.
No. 10.

Figures for the article by A. Danilova, “Materials for the Knowledge of Lower Cretaceous Ammonites from Kopet-Dag.”

New forms: