V. A. Khakhlov,

instructor at the Siberian Technological Institute and docent of Tomsk State University.

Plant Remains of the Olon District

With 15 figures.

PREFACE

The rather numerous and already studied paleophytological collection of the Irkutsk coal-bearing basin was augmented this summer by a small quantity of plant impressions delivered by the geological party of Prof. M. K. Korovin. The material, being too fragmentary and at the same time not especially well preserved, presented great difficulties in detailed study. Nevertheless, I was able to establish a certain number of specific varieties, quite sufficient to illuminate the question of the age of the sandstones separated by Prof. M. K. Korovin into the so-called Olon facies of the Cheremkhovo stage.

The denudational processes strongly developed in the basin area are expressed also in the deep weathering of the rocks that make up the Olon facies. In some parts the weathering has penetrated so deeply into the rock mass that the latter usually consists of loose sands and gravels, cropping out at the present-day surface not only along the banks of the Angara and Belaya rivers, but even on the broad watershed of the Angara—the lower reaches of the Belaya River, where they were mistakenly taken by Prof. K. I. Bogdanovich for Tertiary formations.

A thorough geological survey of the district by Prof. M. K. Korovin’s party and, carried out by him this same summer, a small exploration by trenches revealed, on the right slope of the Angara River, below Ponomareva’s winter settlement, within the loose sandy-gravelly sequence, an argillite horizon typical of the Irkutsk stage, containing plant remains that served as the material for the present article.

The collection studied contains the following plant forms: 1. Cladophlebis kamenkenensis H. Thom; 2. Cladophlebis haiburnensis Lindl. et Hutt. 3. Equisetites ferganensis Sew. 4. Equisetites tenuicostatum n. sp. 5. Baiera longifolia Pom. 6. Baiera sp. 7. Phoenicopsis angustifolia Heer and 8. Desmiophyllum sp.

The occurrence, among the sandstones of the Olon facies, of impressions of typical Jurassic plants compels one to assign the latter to the Jurassic formations, included in the Mesozoic freshwater sequence of the Irkutsk coal-bearing basin, and not to regard it as younger Tertiary deposits, as Prof. K. I. Bogdanovich did on the basis solely of a lithological study of the rocks.

DESCRIPTION OF PLANT FORMS

Filicales.

Cladophlebis kamenken­sis H. Thom.

(Fig. 1, 1-a).

1. Cladophlebis kamenken­sis H. Thom. (14). P. 18. Pl. III; figs. 1—3.

Several fragmentary impressions of fern fronds make it fully possible to assign them to the species Cladophlebis kamenken­sis H. Thom., distinguished by the character of its venation and the external outline of the frond from the closely related species Cladophlebis denticulata (Brgn).

The large, sickle-shaped, curved leaflets are arranged rather closely on the petiole and are about 1 mm wide. Their length is 25 mm; their width—10 mm. The leaflets are always entire-margined. Their upper and lower margins are somewhat bent upward, which gives them a peculiar sickle-like form, gradually narrowing toward the pointed apex. In each leaflet there runs a rather sharply expressed midrib, emerging from the rachis of the frond almost at a right angle, strongly curving and gradually disappearing nearer the apex, where it becomes thinner and more sinuous. From it, at an angle of 45°, depart veins of the second order, situated at a distance of one and a half to two millimeters from one another and alternating with each other on opposite sides of the leaflet. The lateral veins always have dichotomous branching. They undergo dichotomy for the first time not far from their base; one of the branches produced after division is directed somewhat forward toward the end of the leaf and soon undergoes a second forked division. The second branch is directed, approximately, at an angle of 30° to the petiole and, after passing a somewhat greater distance than the first, likewise divides into two equal branches. The veins obtained as a result of the double branching run parallel to one another. The character of the venation can be better clarified from the image of the leaflet enlarged twofold and given in Fig. 1-a.

By the presence of twice-dichotomizing veins, with the exception of some located closer to the apex, the leaflets described differ sharply from the closely related species Cladophlebis denticulata (Brgn) and very much resemble the specimens described by Thomas from the Jurassic deposits of Kamenka in the Izyum district under the new specific name Cladophlebis kamenken­sis H. Thom. In their external form and character of venation, the specimens of the Olon facies and of Kamenka are completely identical, but in their dimensions they differ somewhat from one another. Thus, the greatest length of the leaflets described by Thomas is 15—18 mm, whereas our specimens reach 25 mm in length. But, taking into account the fact of the existence of individual variability in plant forms in general and, in particular, in the genus Cladophlebis (Brgn), we must with complete confidence assign our specimens to the species Cladophlebis kamenken­sis H. Thom., emphasizing their first occurrence among the fossil floras of Siberia.

Cladophlebis haiburnensis Lindl. et Hutt.

(Fig. 2—3).

1. Cladophlebis haiburnensis L. et Hutt. A. Seward. (11). P. 26, pl. II, fig. 34; pl. VI, figs. 35, 36, 41 and 44.

1. Cladophlebis haiburnensis L. et Hutt. A. Seward. (16). P. 3, pl. I; pl. II, figs. 7 and 8; pl. III.

2. Cladophlebis haiburnensis L. et Hutt. A. Turutanova. (15). P. 4, figs. 3 and 5.

In the small paleobotanical collection from the Olon Formation of the Irkutsk coal basin, there is a comparatively large number of impressions of fragments of leaves belonging to the species Cladophlebis haiburnensis L. et Hutt. Individual fragments of them occur sometimes completely isolated, sometimes directly attached to the petiole. The best of them are shown in figs. 2–3.

Figure 3 is an impression of rather poor preservation, with secondary veins expressed somewhat clearly in places. The petiole is at most one millimeter thick. The separate pinnae are arranged almost oppositely, are slightly inclined toward the petiole, and are situated at a short distance from one another. They are almost always with parallel margins; only closer to the apex do they begin gradually to narrow and end either in a semicircle or even acutely. The midvein, as it approaches the top of the pinna, begins to break up into a whole series of veins of the second order with dichotomous branching. From the median nerve, at a certain acute angle, depart veins of the second order with twice dichotomous branching.

The largest leaflets are represented in fig. 3. The typical venation for the species Cladophlebis haiburnensis L. et Hutt., preserved here and there, leaves no doubt as to the correctness of the determination of the specimen. The width of the separate pinnae reaches 8 mm. The leaflets are alternate and are arranged almost at a right angle to the petiole. The median nerve is sufficiently clear. From it depart veins of the second order with dichotomous branching not far from the base. They undergo secondary dichotomous branching after passing some distance, and even then not always. Thus it happens that some veins do not undergo secondary branching at all, and both of their branches, obtained as a result of the first division, follow parallel to one another as far as the outer outline of the leaf. This can be observed on the lower right pinna of fig. 3. Similar pinnae and pinnules are cited by Prof. A. Seward in forms of Cladophlebis haiburnensis Lindl. et Hutt. in his description of fossil plants of the Caucasus and Turkestan.

The closer arrangement of several branching veins, together with their broader and less sickle-shaped external form, gives sufficient grounds to distinguish them from the closely related species Cladophlebis denticulata Brgn. But the varied venation within the species Cladophlebis haiburnensis L. et Hutt. itself suggests that more than one natural group of plants is included in this species. Taking into account the fact of individual variability of the leaves of this fern, and considering that the characters which we use in dividing the genus into separate species are far from constant but, on the contrary, are subject to certain changes, it would be quite premature to single out any independent groups from the broad species Cladophlebis haiburnensis L. et Hutt.; this can be done only after clarifying at least the approximate limits of variability of fern leaves, without which even the division of the genus Cladophlebis Brgn. itself into separate species appears a very difficult and sometimes not properly solvable task.

The species Cladophlebis haiburnensis Lindl. et Hutt. has a broad geographical distribution and is considered a typical Jurassic fern.

Equisetales.

Equisetites ferganensis Sew.

(Figs. 4, 5, 9).

1. Equisetites ferganensis Sew. A. Seward. (11). P. 18, pl. II, figs. 23—31; pl. 3, figs. 6, 1.
2. Equisetites ferganensis Sew. V. Vakhlov. (17). P. 7, figs. 6—16.

The new stone material, delivered in the current year 1924 by Prof. M. Korovin, is characterized only by the presence of structureless pith casts of horsetail trees. In all impressions of the internal cavities the ribs pass through the nodes without changing their direction, whereby they very closely resemble the piths of horsetails from the Fergana region and Irkutsk Province, described under the name Equisetites ferganensis Sew., in which, with typical leaf sheaths of the Equisetites type, there are internal casts with a structure of the Phyllotheca or Schizoneura type. On most impressions we observe grooves 1 mm wide, i.e. the ribs are situated at intervals of 1 mm. A certain exception is presented by the specimen shown in Fig. 4, where we observe rather numerous ribs passing through the node, likewise without changing their direction, and situated at a distance somewhat less than 1 mm. The width of the grooves is approximately 0.8 mm. Such variations, apparently, may occur in the species Equisetites ferganensis Sew. Thus Prof. A. Seward, in describing specimens from the Fergana region, mentions structureless casts of the internal cavities with grooves reaching 1—2 mm in width. In Fig. 5 an impression of a slender branch is presented, 4 mm wide and with 4 grooves. This impression, together with others, proves that the distance between the ribs is maintained on branches of the most varied diameter.

As for the length of the internodes, the actual material is insufficient for forming an adequate idea. It may be thought that the occurrence on some specimens of a node and of a part of the stem above it up to 40 mm long gives some grounds for considering that the internodes were comparatively long, approaching those dimensions which we could observe in specimens from Fergana and the Irkutsk coal basin.

Among the small collection there is a considerable number of impressions of root offshoots, shown in Fig. 9. Similar formations were mentioned many times in the previous work devoted to the description of the fossil flora of the Irkutsk coal basin. Their joint occurrence with the underground parts of horsetail stems leaves no doubt as to the correctness of the determination of such fragments.

The species Equisetites ferganensis Sew. has so far been found in Jurassic deposits of Turkestan and Irkutsk Province, being, apparently, a typical Jurassic horsetail of the Angara continent.

Equisetites tenuicostatum n. sp.

(Figs. 6–8).

Among the structureless piths of horsetails in the collection there are several specimens differing in their external appearance from the piths of Equisetites ferganensis Sew. The width of their longitudinal grooves is so slight that the impression is created of a very fine and dense longitudinal striation covering the surface not only of slender but also of fairly large parts of the stem. Usually the width of the grooves is 0.3 mm, i.e. at a distance of 1 mm there pass 4 ribs. A certain number of impressions are shown in Figs. 6—8. In Fig. 6 we have

we have an impression of a thin branch, only 6 mm wide, and on it ribs pass at a distance of 0.3 mm. Fig. 7 represents still thinner branches of horsetail with ribs of the same width. In Fig. 8 we observe a comparatively thick branch, 24 mm thick, on which the ribs are arranged as densely as on the thin branches. The grooves and ribs on all the specimens where there are impressions of nodes pass through the latter without changing their direction, which indicates the absence of branching of the vascular bundles in the node and brings, to a certain degree, our casts closer to the pith casts of the type Phyllotheca and Schizoneura, which we have already observed in the species Equisetites ferganensis Sew., together with typical leaf sheaths of horsetail habit.

The pith casts found in the sandstones of the Olon facies of the Irkutsk coal basin do not provide exhaustive material for a complete characterization of this plant; but this still does not remove the possibility of distinguishing the given forms, by the originality in the arrangement of their vascular bundles, as a new species, which I name Equisetites tenuicostatum n. sp., according to the character of the very densely arranged ribs. In describing the specimens from the Fergana region, Prof. A. Seward cites, on plate 3, figs. 9—J (11), an internal cast with very densely arranged ribs, as though entirely resembling our specimens. But we can speak of the complete identity of the casts only when we have at our disposal some numerical material. Measuring the width of the grooves on the plate, we see that they fully correspond to our dimensions, i.e. the ribs pass at a distance of 0.3 mm. Thus, if we were to regard the internal cast assigned by A. Seward to the species Equisetites ferganensis Sew. and differing from the usual internal cores by a denser arrangement of the ribs as identical with our specimens from the Irkutsk basin, then thereby our conception of the new horsetail plant would be somewhat supplemented, at least with respect to the length of the internodes. However, we shall not insist on the identification of these specimens, if only because in the description of A. Seward’s figures there is the expression “slightly reduced,” which compels one to treat with some caution the illustration, the true dimensions of which are not given by the author in describing the specimen.

Impressions of internal, structureless casts from Irkutsk Province and the Fergana region indicate a combination of vascular bundles of the Phyllotheca and Schizoneura type with leaf sheaths of true horsetails—a circumstance which undoubtedly points to the phylogenetic connection of Equisetites tenuicostatum n. sp. and Equisetites ferganensis Sew. with typical horsetails of the Gondwanan flora. These forms are plants that emerged from typical Gondwanan horsetails by the gradual modification and transformation, on the territory of the Angara continent, of individual leaf segments into the leaf sheaths of true horsetails.

Ginkgoales.

Baiera longifolia Pom.

(Figs. 10—11).

1. Baiera longifolia Pom. O. Heer. (21). P. 59. Pl. 7, fig. 2, and pl. VIII.

2. Baiera longifolia Pom. O. Heer; V. Khakhlov. (16). P. 7, figs. 10—15.

Studying the plant remains of Irkutsk Province and the Amur region, Prof. O. Heer as early as 1876 emphasized the very great diversity in the character of the external outline and dissection of the leaf blade in the species Baiera

longifolia Pom., and even attempted to classify them into separate groups. Thus, he distinguished the following three principal groups: I. Foliis dichotomis, quadrilobis, II. Foliis quinquelobis, and III. Foliis dichotomis, sexlobis. The first group was, in turn, further divided into two subgroups. Such an artificial subdivision, of course, could have no practical significance, and we see that almost 50 years have already passed since the corresponding work of Prof. O. Heer was published, and meanwhile there is not a single author who, in working up fossil material, has made use of these minor subdivisions. On the contrary, more and more often in the monographic literature we find indications of the strong individual variability of the leaves of the genus Baiera F. Br., producing a considerable diversity of forms, between which it is impossible to draw any definite boundaries; hence the division of the genus itself into separate species always presents great difficulties and cannot always be considered entirely correct.

The fragments of leaves shown in Figs. 10 and 11 represent the best specimens of the collection. Fig. 10 shows an impression of a leaf lobe with a dichotomous division into two unequal parts. The left lobe is 4 mm wide and contains three parallel and rather sharp veins; the right one is 5 mm wide and contains 4 parallel nerves. The impression shown in Fig. 11 characterizes fragments of leaf segments 4–5 mm wide, through which pass 4 or 5 thin parallel veins.

With a considerable degree of probability our impressions may be identified with the typical form from the Irkutsk coal-bearing basin, Baiera longifolia Pom., cited by Prof. O. Heer from the Angara River, Ust-Baley, and by me from the Cheremkhovskaya and Sukhovskaya formations. To some extent they also resemble the broad-lobed forms of Baiera Czekanowskiana Heer, which are likewise widely distributed in the Irkutsk basin. But their complete identity with the impressions given by Prof. O. Heer in pl. 7, figs. 2 and 3, and also in figs. 1–10 of plate 8 (21.), compels us to leave them under the species name Baiera longifolia Pom.

Baiera longifolia Pom. is especially characteristic of the Upper Jurassic deposits of Western Europe. It occurs rather frequently in those deposits of Eastern Siberia and the Far East which until recently were generally regarded as Middle Jurassic.

Baiera sp.

(Fig. 12).

An overly fragmentary remnant of a leaf blade with well-preserved venation is given by me in Fig. 12. A leaf lobe with parallel margins is 4 mm wide and reaches 45 mm in length. Near it, above, there is a small fragment of a leaf lappet, whose length, with a width of 5 mm, is 12 mm. In both fragments there pass 4 parallel and relatively thin nerves, not always visible. At first these impressions were taken by me for leaves of Phoenicopsis speciosa Heer, but the presence of very fine intermediate venation, characteristic of the genus Baiera F. Br., compelled me to leave these impressions under the name Baiera sp. By the width of the leaf lappets they may be referred either to the species Baiera longifolia Pom., or Baiera Czekanowskiana Heer, or Baiera gracilis Bunb. The considerable length of the lappets indicates their belonging rather to the species Baiera longifolia Pom., but the finer veins of the first order covering the leaf lappet speak for a certain distinctness of these forms.

Ginkgoales incertae sedis.

Phoenicopsis angustifolia Heer.

(Fig. 13).

1. Phoenicopsis angustifolia Heer. A. Seward (11). P. 34, pl. 8, figs. 69 and 60.
2. Phoenicopsis angustifolia Heer. (21). P. 51, pl. 1, fig. 1; pl. 2, fig. 3b.
3. Phoenicopsis angustifolia V. A. Vakhrameev (16). P. 18, figs. 26–32.

Only a single impression from the entire collection of the Olon district can be referred to the species Phoenicopsis angustifolia Heer. It is shown in fig. 13. A bundle of not very well preserved leaves, no more than 3 mm wide, is typical of the Irkutsk Jurassic. The venation is inconspicuous, but the insignificant width of the leaf blades, with their limited length, which on the impression does not exceed 60 mm, and the clearly visible arrangement of them in different planes, give full grounds for identifying it as Phoenicopsis angustifolia Heer. Moreover, the specimen is entirely identical with certain impressions already described from the Irkutsk coal basin.

The species Phoenicopsis angustifolia Heer has a wide geographical distribution and is considered an especially characteristic member of Upper Jurassic floras.

Plantae incertae sedis.

Desmiophyllum sp.

(figs. 14, 15)

1. Desmiophyllum sp. A. Seward. (13). P. 15, pl. 2, figs. 16, 16-a,
2. Podozamites gramineus Heer. O. Heer. (21) P. 46; pl. 4, fig. 13.

Under the generic name Desmiophyllum Lesq. are usually described long leaves with parallel margins, through which run very sharp and few parallel veins. Linear leaves are always found isolated, so that it is not even possible to ascertain their relation to shoots. By the character of their coarse venation these forms cannot be unambiguously assigned to the genus Phoenicopsis Heer, Podozamites F. Br., or others.

Prof. A. Seward, in determining fossil plants from the Tyrma River of the Amur Region, uses the generic name Desmiophyllum Lesq. to designate very long leaves with strongly projecting veins. Our specimens, shown in figs. 14, 15, are quite close to A. Seward’s illustration. In fig. 14 we have the largest fragment of a leaf, 50 mm long and 3.5 mm wide, its surface being covered with three parallel veins so sharp that they may be taken for ribs of horsetails. Fig. 15 shows an impression of a leaf fragment 48 mm long and 4 mm wide. Through it pass 4 parallel and likewise very sharp veins. On both specimens no intermediate venation is observed.

The leaves somewhat recall the specimens figured by O. Heer (22) on pl. 7, figs. 11, 12 under the name Leptostrobus rigida Heer. There is complete similarity with the leaf given by the same author on pl. 14, fig. 13 (21) under the name Podozamites gramineus Heer, which reaches 94 mm in length and 3 mm in width; it gradually narrows toward the end, and through it run 4 parallel and rather sharp veins. There is no similarity of this Heer impression with leaves of the genus Podozamites F. Br., and the designation of our

assigning the specimens the generic name Podozamites F. Br. would be highly erroneous, which is why they are determined as Desmiophyllum sp. We are not in a position to make a more precise specific determination because of the lack of a sufficient number of characteristic features. The number of sharp nerves and the width of the leaf fragments, of course, cannot be regarded as objective characters for distinguishing small independent systematic units; therefore the attempt at an artificial division of the genus into smaller units would be premature and of no practical significance.

CONCLUDING RESULTS.

The study of the fossil plants of the Irkutsk coal basin indicates a considerable diversity of the flora and its wealth of new species. It includes representatives of almost all the principal groups of plants that flourished in Jurassic time, and certain representatives, for example Czekanowskia Heer, Phoenicopsis Heer, ferns, and others, occur in such enormous quantities that their impressions fill entire beds of the freshwater deposits of the Irkutsk series.

The material additionally supplied from the Olon district this year, in processed form, consists of the following plant forms:

1. Cladophlebis kamenkenensis H. Thom.
2. Cladophlebis haiburnensis Lindl. et Hutt.
3. Equisetites ferganensis Sew.
4. Equisetites tenuicostatum n. sp.
5. Baiera longifolia Pom.
6. Baiera sp.
7. Phoenicopsis angustifolia Heer.
8. Desmiophyllum sp.

Among the eight species of plant remains we have one new species, Equisetites tenuicostatum n. sp. The species Cladophlebis kamenkenensis H. Thom. and Desmiophyllum sp. are encountered for the first time in the deposits of the Irkutsk basin. The remaining forms are typical Jurassic plants of Irkutsk Province and partly of the Far East.

The species Equisetites tenuicostatum n. sp. is characterized by very fine furrows and ribs passing through the nodes without changing their direction, which to some extent brings it closer to Equisetites ferganensis Sew., which combines the leaf sheaths of the Equisetites type with the vascular bundles of horsetails of the Gondwana flora.

The species Cladophlebis kamenkenensis H. Thom., encountered for the first time in the Irkutsk series, differs from the specimens from Kamenka in the Izyum district by somewhat larger dimensions. There is no need to speak of its geological distribution, since it was only recently established by Thomas and its age limits cannot be considered clarified.

Forms of Desmiophyllum sp. similar to our impressions were described by A. Seward and O. Heer from the Amur region. The beds containing the Amur plants, according to A. Seward, recall the flora of rich Middle Jurassic collections. Heer, however, considers them members of the Bathonian flora.

Thus, for determining the more precise age of the deposits of the Olon district, there remains at our disposal a comparatively small number of plant forms. Comparison of them with the fossil plants of the Irkutsk coal basin shows that a similar flora can with equal probability be identified with the flora of the Sukhovskaya and Cheremkhovskaya formations.

The excessively small number of species does not permit a more exact decision on the question of the age of the sandstones of the Olon district. But it becomes quite clear that the pebble beds are formations entering into—

included in the freshwater sequence of Mesozoic deposits, which in their thicker part belong to the upper division of the Jurassic.

The description of such a small collection, of course, in itself has no great significance from the general paleobotanical point of view, but it nevertheless provides some material for supplementing our ideas about the composition of the fossil flora of the Irkutsk coal basin. In addition, we may hope that similar notes may provide grounds for drawing interesting conclusions in the field of the paleogeography of plants and may help to clarify the comparative evaluation of plant species as guide fossils, at least within the territory of Siberia and the Far East.

Explanation of the Figures.

1. Cladophlebis kamenkensis H. Thom.
   1-a. A leaflet of Cladophlebis kamenkensis H. Th., enlarged twofold.
   2–3. Cladophlebis haiburnensis Lindl. et Hutt.
   4–5. Equisetites ferganensis Sew.
   6–8. Equisetites tenuicostatum n. sp.
2. Root formations of Equisetites ferganensis Sew.
   10–11. Baiera longifolia Pom.
3. Baiera sp.
4. Phoenicopsis angustifolia Pom.
   14–15. Desmiophyllum sp.

Bibliography.

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Plate I

Appendix to the description of fossil plant remains.

Fig. 1.

Fig. 2.

Fig. 3.

Fig. 1a.

Fig. 4.

Fig. 5.

Fig. 6.

Fig. 7.

Fig. 8.

Fig. 9.

V. A. Kakhlov. Plant remains of the Olon District.

Plate 2.

Fig. 10

Fig. 11

Fig. 13

Fig. 12

Fig. 14

Fig. 15

V. A. Krylov. Plant remains of the Olonets District.

Sheet O. Z. S. Type 500 copies. OKRNL No. 920, VI-26, p. 14.

1. Turutanova, A. Materials for the study of the fossil flora of the Cheremkhovo coal basin. Jurassic remains. Izv. Sib. Geol. Kom. Vol. I, Issue 5. 1920.

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3. Kakhlov, V. Fossil plants of the Irkutsk coal basin. Izv. Sib. Otd. Geol. Kom. Vol. 4, Issue 2. 1924.

4. Seward, A., and N. Thomas. Jurassic plants from Balagansk Uezd, Irk. Gubernia. Tr. Geol. Kom-ta. New Series. Issue 73. 1911.

5. Geyler, H. Über fossilen Pflanzen aus der Juraformation Japans. Palaeontographica. 24. 1876–7.

6. Heer, O. Die Kreide—Flora der arctischen Zone. 1875.

7. Heer, O. Beiträge zur Jura—Flora Ostsibiriens und des Amurlandes. 1877.

8. Heer, O. Beiträge zur fossilen Flora Sibiriens und des Amurlandes. 1878.

9. Heer, O. Nachträge zur Jura—Flora Sibiriens. 1880.

10. Krasser, F. Pflanzen aus Transbaikalien, der Mongolei und Mandschurei. 1905.

11. Krasser, F. Die von Obrutschew in China und Central-Asien 1893—94 gesammelten fossilen Pflanzen. 1900.

12. Nathorst, A. Über Trias und Jurapflanzen von der Insel Kotelny. 1907.

13. Saffeld, H. Beiträge zur Kenntnis jurassischer Pflanzenreste, aus Norddeutschland. Palaeontographica LVI, 1909.

14. Schenk, A. Jurassische Pflanzen. China. Band IV. F. von Richthofen. 1883.

15. Schmalhausen, J. Beiträge zur Jura-Flora Russlands. Memoir. de l’Ac. Imp. de Science de S-Pétersb. T. XXVII.