Fossil plants, Vol. 3

Occasional reference is made to Cycadean fronds in the account of flowers and stems but it is seldom that genera or species founded on leaves can be definitely correlated with particular types of reproductive organs or stems. As in the case of Ferns and Pteridosperms so also with detached leaves believed to be Cycadean, a large number of generic names have been employed for impressions which afford no information with regard to anatomical characters except, in some of the more favourably preserved specimens, a few facts as to the epidermal cells. Though association often suggests original connexion it is inadvisable except in well established cases to extend to fronds generic terms based on reproductive shoots. The designation Zamites has long been used for fronds that are clearly not closely related to recent species of Zamia, and were it not an old established genus the significance of which is not likely to be misunderstood, it would be wiser to substitute for it some name implying no affinity with any existing type. On the other hand the employment by some authors of such generic names as Encephalartos and Ceratozamia is not warranted by the evidence furnished by the imperfect material. Prof. Newberry[1424] described as Encephalartos? denticulatus a piece of a frond from Rhaetic beds in Honduras characterised by lanceolate pinnae (30 × 6 mm.) gradually narrowed towards the acute apex and abruptly contracted at the base: the method of attachment of the pinnae appears to agree with that in the genus Zamites. In this case there is no valid reason for assuming a relationship with Encephalartos or with any recent type. An impression from Lower Cretaceous, Dakota, beds in Kansas described as Encephalartos cretaceus Knowlt. ex Lesq. ms.[1425] consists of a piece of lamina, 9 × 4 cm., obovate-oblong and with a cuneate base, a serrate margin and thick diverging veins: the specimen is too incomplete to serve as a record of any Cycadean genus. The generic name Encephalartopsis was applied by Fontaine[1426] to some imperfect pinnae from the Potomac beds characterised by a linear-elliptical lamina with a spinous margin and slightly diverging and occasionally anastomosing veins. The figured examples of the type-species, E. nervosa, suggest pinnae like those of Ctenis; but in the absence of a rachis the method of attachment of the segments cannot be ascertained. Saporta[1427] named a specimen from the Miocene flora of Koumi, Greece, Encephalartos Gorceixianus because of its resemblance in habit to some species of the recent genus; but the designation Zamites would be more appropriate. Ettingshausen recorded an imperfect impression of a pinna from Tertiary rocks in Styria as Ceratozamia Hofmanni[1428] although it is by no means certain that the fragment is even Cycadean. The genus Taeniopteris was described in the second volume of this book as probably a Pteridophyte, though of uncertain systematic position: it has, however, been shown by Mr Thomas[1429] that the Jurassic species T. vittata was almost certainly borne on a stem with reproductive organs constructed on the Bennettitalean plan. Further research may enable us to fix the position of other species but as yet T. vittata is the only representative of the genus which there is good reason for assigning to the Bennettitales.

It is undoubtedly true that Cycadean plants, using the term in a wide sense to include the Bennettitales as well as the Cycadales, bulked largely in Upper Triassic, Rhaetic, Jurassic-Wealden floras; the Bennettitales probably reached their maximum development as regards wealth of form and geographical range in the latter part of the Jurassic period and in the earliest phase of the Cretaceous epoch. In Triassic floras Cycadean plants are represented almost solely by fronds but the very close resemblance between Keuper species and forms that in Jurassic rocks are found in association with fertile shoots leaves little doubt as to the affinity of Keuper and Rhaetic species.

The evidence obtained from Permo-Carboniferous strata is much more meagre, at least as regards Cycadean leaves: the occurrence of certain morphological Cycadean features is revealed by petrified vegetative organs of Palaeozoic plants, and the Cycadean plan of organisation is conspicuous in many Carboniferous and Permian seeds. The discovery of frond-impressions identical in external characters with Mesozoic genera may be accepted as a substantial indication that genera already existed possessing foliage of the Cycadean type, though we have no certain information with regard to the nature of the other organs of the parent-plants. A few examples of Palaeozoic species are included among those selected in illustration of the different genera, namely Plagiozamites Planchardi, Sphenozamites Rochei, Pterophyllum Fayoli, P. Cambryi: among other recorded instances of Palaeozoic species are Pterophyllum Cottaeanum Gutb.[1430], a Permian type similar in habit to Ctenis but without anastomosing veins, a feature in which it resembles Pseudoctenis; the Carboniferous species Pterophyllum inflexum Eich.[1431] from the Altai mountains, transferred by Zeiller to Dioonites; P. blechnoides Sand.[1432] from the Stephanian of Oppenau; Pterophyllum Grand’Euryanum[1433] from Upper Carboniferous beds in France, and P. gonorrachis Goepp.[1434] from Silesia. An examination of the type-specimens of the Carboniferous species Cycadites gyrosus Goepp. and C. taxodinus Goepp.[1435] in the Breslau Museum led me to regard the material as too imperfect to determine.

A conclusion that is forced upon us by a consideration of the geological range of Cycadean fronds is that at the close of the Wealden period, a period very closely linked in the character of the vegetation with the preceding Jurassic floras, there appears to have been a relatively sudden decrease in the number of members of the Cycadophyta: the decline in the fortunes of Cycadean plants is coincident with the rise and remarkably rapid extension of the Angiosperms. From Middle and Upper Cretaceous and from Tertiary beds very few Cycadean remains have been obtained and many of them are represented by fragmentary fossils that afford no definite evidence of affinity to recent genera. The antiquity of the Cycadales, that is the section represented by existing Cycads, cannot be determined; but it would seem probable that if the Cycads apart from the Bennettitales existed in Jurassic and Lower Cretaceous floras they occupied a very subordinate position in comparison with the extinct Bennettitales. There are no data pointing to any widespread occurrence of the Cycadales in the Northern Hemisphere in Tertiary times at all comparable with the geographical range of Tertiary ancestors of the solitary survivor of the Ginkgoales.

The following records of Tertiary Cycadean fronds illustrate the paucity of the records. Reference has already been made to Encephalartos Gorceixianus Sap. of Miocene age, a species that has no claim to be regarded as an example of the recent South African genus. The specimen described by Saporta and Marion as ? Zamites palaeocenicus[1436] from the Eocene of Gelinden is too imperfect to serve as a trustworthy record. A more satisfactory species, similar in habit to Zamites gigas, is that on which Saporta founded the species Zamites epibius[1437] from Lower Miocene beds at Bonnieux (Vaucluse), France. Another Tertiary species is mentioned by Krasser[1438] from Pliocene strata in Brazil as Zamia praecedens Krass. ex Ett. MS. Ettingshausen has described a Tertiary species from New South Wales, either Lower Miocene or Upper Eocene in age, as Anomozamites Muelleri[1439], characterised by truncate segments with simple veins and set obliquely to the rachis.

While certain form-genera of fronds can only be referred to the Cycadophyta, in other cases it is possible to assign fronds to a section of this comprehensive group characterised by a particular type of fertile shoot and by certain well defined epidermal features.

The investigation of the cuticular structure of various Cycadean fronds by Nathorst[1440] and especially by Mr Thomas[1441] has supplied a basis of classification which affords the best criterion of affinity so far available. The majority of fronds are placed in the Bennettitales while the three genera Ctenis, Nilssonia, and Ctenopteris (or Ptilozamites[1442]) are placed in the Nilssoniales.

I. Bennettitales. Epidermal cells characterised by sinuous walls and generally rectangular; the cuticle is thin; the stomata, confined to the lower surface of the pinnae, tend to be arranged at right-angles to the veins and are on a level with the epidermis or very slightly depressed; two large laterally placed subsidiary cells more or less surround the guard-cells and these are provided with thickenings of a definite shape (figs. 594, 609).

Genera: Ptilophyllum, Zamites, Otozamites, Dictyozamites, Pterophyllum and Anomozamites, Taeniopteris, Pseudocycas.

II. Nilssoniales. Epidermal cells with straight walls, not sinuous, irregular in form, rounded, hexagonal, or rectangular; the stomata are below the level of the epidermis; the cuticle may be thin or thick. There is no regular arrangement of the stomata; the guard-cells are surrounded by 6–8 subsidiary cells (fig. 625) which often form an overarching canopy; thickening lamellae like those on the guard-cells of the Bennettitales are seldom present.

Genera: Nilssonia, Ctenis, Ctenopteris.

It is a noteworthy fact that the representatives of the smaller group, the Nilssoniales, in their cuticular features, are more akin than the Bennettitales to modern Cycads. Until definite evidence is obtained as to the nature of the reproductive organs of Nilssonia, Ctenis, and Ctenopteris it is impossible to say how closely these genera agree in essential characters with existing members of the Cycadales. If, as has been suggested, the fertile shoots known as Beania[1444] belong to Nilssonia their resemblance in plan of construction to the cones of recent genera, much greater than in the case of the flowers of the Bennettitales, is in accordance with the evidence of the epidermal characters.

Reference was made in the second Volume of this book to several genera founded on fronds which through lack of evidence as to the nature of the reproductive organs cannot be assigned with certainty either to Ferns or Cycads: it was stated that the genera Ptilozamites and Ctenopteris are probably Cycadean, and the structure of the epidermal cells in the latter genus lends support to this view[1445]. Among other genera of doubtful position not included in the following descriptions of fronds is Zamiopsis of Fontaine[1446] founded on large compound fronds from the Potomac formation: the venation and form of the pinnae are more Fern-like than in Ctenopteris, but in general habit the two genera are not very dissimilar. The generic name Zamiopsis is misleading as the species bear no resemblance to Zamia or Zamites.

I. Bennettitales.

PTILOPHYLLUM. Morris.

The generic name Ptilophyllum was instituted in 1840 for some specimens of pinnate fronds from Cutch: in this genus Morris[1447] included with the Indian leaves the English Jurassic species Pterophyllum pecten Lind. and Hutt.[1448] (figs. 587, etc.) and some other forms. He defined Ptilophyllum as follows: ‘Fronds pinnate; pinnae closely approximated, linear, lanceolate, more or less elongate, imbricate at the base, attached obliquely; base semicircular or rounded; veins equal, slender, parallel.’ Morris adds that he instituted a new genus in preference to Zamites because of the ‘oblique insertion of the pinnae and their overlapping each other at the base.’ In a later paper Morris[1449] states that the pinnae of Ptilophyllum fronds are ‘sometimes auriculed in the upper and sometimes in the lower part’ of the base of the lamina. In his catalogue[1450] he adopted Endlicher’s genus Palaeozamia instead of Ptilophyllum. Without discussing the generic nomenclature adopted by various authors for the Indian types and similar fronds it is important to refer briefly to the treatment of Morris’s species by Oldham and Morris and by Feistmantel. In the first of the series of Memoirs on Gondwana floras[1451] Ptilophyllum is retained for a section of Palaeozamia together with Otozamites and Sphenozamites as other sectional subdivisions: in the subgenus Ptilophyllum are included Palaeozamia acutifolia and P. cutchensis (fig. 588, A, C), also P. affinis, P. rigida, and P. bengalensis. The last species is in all probability an Otozamites: P. affinis and P. rigida are almost certainly indistinguishable from P. cutchensis. Feistmantel[1452] dealt in detail with the genus Ptilophyllum: he wrote, ‘with Schimper and Schenk I therefore look upon this genus as an Indian type especially characterised by its ... more or less slender leaves, angustate towards the apex and base, and petiolate, with regularly adfixed leaflets.... The leaflets are equal to each other, for the most part elongate linear, and auriculate and free at the upper angle at the base, but adfixed at the lower angle, and each is decurrent behind the upper angle of the leaflet next below it, thus the leaflets are almost imbricate. The veins are rather numerous, simple, and forked, and more or less divergent[1453].’ Feistmantel distinguishes certain varieties of P. cutchense (fig. 588, A, C), none of which appear to be well defined. A specimen from the Rajmahal Hills with unusually long pinnae, the frond having a breadth of 8 cm., is described as Ptilophyllum acutifolium var. maximum[1454], but it differs in no important feature from the smaller and commoner form. The next point to be considered is the variability of certain species referred by Feistmantel to Otozamites. He figures specimens from the Jabalpur group as O. Hislopi Feist. ex Old. MS., O. gracilis (Kurr), O. angustatus Feist. (fig. 588, B) and O. distans[1455]. An examination of the figured specimens leads me to regard O. Hislopi and O. gracilis as identical with the Ptilophyllum fronds: the pinnae exhibit no distinguishing features and there is no reason for a specific, still less a generic, separation. Otozamites angustatus is indistinguishable from Otozamites sp. as figured from the Madras coast and from Ptilophyllum cutchense, P. cutchense var. curvifolium and var. minimum. The drawings reproduced in fig. 6a, Pl. x. of the Madras flora[1456] and in fig. 8a, Pl. vi. of the Jabalpur flora[1457] showing auriculate bases are inaccurate: in all the fronds named the pinnae are straight with rounded edges precisely as in Ptilophyllum. The conclusion forced upon me by a comparison of the actual specimens is that the Indian fronds are not separable into well-defined species and should all be included in Ptilophyllum cutchense. Moreover in this comprehensive species should be included the specimens described by Feistmantel as Otozamites Hislopi (fig. 589), O. angustatus, and O. gracilis. It may well be that a more detailed investigation of the numerous forms comprised in this protean species, particularly if specimens are obtained from which cuticular preparations can be made, may lead to the recognition of additional species or well-defined varieties. The resemblance between the various forms of P. pecten from the Jurassic strata of Yorkshire and those of P. cutchense from India is very striking, and at least in many cases no specific separation is possible so far at least as the form of the fronds and pinnae is concerned. The occasional close association of Ptilophyllum fronds and Williamsonia flowers is an important agreement between the English and Indian fronds (fig. 590).

In the first part of the Catalogue of Jurassic plants from Yorkshire the opinion was expressed[1458], based on an examination of Morris’s type-specimen of Ptilophyllum cutchense and of a large number of English and other fronds identical with or closely allied to Pterophyllum pecten Lind. and Hutt., that the Indian and European fronds belong to the same genus. In a later paper[1459] it was maintained that P. cutchense and P. acutifolium are probably identical with the English type, and a drawing was published—reproduced in fig. 591—of Morris’s type-specimen. Dr Halle[1460] has discussed the genus Ptilophyllum and his investigations lead him to a different conclusion; he, like Zeiller and some other authors, employs Ptilophyllum in Feistmantel’s sense. The pinna-base is said to agree in its asymmetrical form with that in Otozamites, while it differs from the symmetrical base of Zamites pinnae. In Ptilophyllum both edges of the pinna-base are said to bend down in joining the rachis; at the upper corner the base thus becomes rounded and for some distance free from the rachis; it is also sometimes a little auriculate; at the lower edge the pinna is decurrent on the upper surface of the rachis. In a subsequent paper Halle[1461] repeats the view that the decurrence of the pinnae by their lower edges is an important distinguishing feature of Ptilophyllum, thus agreeing with Feistmantel whose illustrations appear to be confirmatory. The drawings in Feistmantel’s memoirs are, however, misleading and in some cases incorrect. An examination of a photograph of Morris’s type-specimen of P. cutchense led Halle to conclude that the two edges of the pinna-base bend downwards on joining the rachis as described by Feistmantel. This feature is not shown in the drawing reproduced in fig. 591: it is clear that either the drawing is incorrect or that there has been some mistake in the interpretation of the photograph. Through the courtesy of Dr Halle I have been able to examine the actual print: when viewed in its correct position the two edges of the pinnae appear to bend down as described by Halle, but if it is examined in the reverse position the lower angle of the pinnae is seen to be slightly rounded as in fig. 591, the apparent decurrence being due to a confusion between the appressed lower edge of one pinna, which is faintly shown, and the stronger downward trend of the upper edge of the pinna next below. The upper edges of the pinnae are more prominent because they are less appressed to the rachis while the lower half of the base is closer to the rachis and is frequently, though not in Morris’s specimen, overlapped by the upper edge of the next lower pinna. A re-examination of the type-specimen in the British Museum confirms this interpretation. The pinnae of Ptilophyllum are characterised by their attachment to the upper face of the rachis which they almost completely cover; the upper angle is rounded and in a few cases auriculate (fig. 592); the lower angle of the base is slightly rounded and not infrequently hidden by the imbrication of the adjacent pinna; it is occasionally auriculate (fig. 593). The pinnae are attached by nearly the whole base, but the upper angle is free. The veins are parallel, sub-parallel or, especially in the proximal portion of the lamina, oblique. The pinnae are linear, varying considerably in relation of length to breadth and in the form of the apex; they are straight or more or less falcate. The epidermal cells of such Ptilophyllum fronds as have been examined are characterised by strongly looped or sinuous walls; the stomata, confined to the lower surface, are roughly circular and the guard-cells are at right-angles to the veins and not appreciably sunk. Fig. 594 represents the appearance of a stoma in surface-view: ‘on either side of the central slit-like pore are two elliptical or hemispherical structures; they are somewhat flattened when they abut on the pore, and have rounded ends.... Between these and the subsidiary cells lie two other thickened patches, more or less hemispherical in shape, and apparently overlying the central structures.’ On the analogy of similar appearances in recent Cycads Mr Thomas[1462] interprets the two pairs of thickened patches as belonging to the upper and lower sides of the highly inclined guard-cells. This author calls special attention to the abundance on some of the fronds included in the aggregate species P. pecten of regular rows of circular hair-scars preserved as small annulate projections, ·03–·04 mm. in diameter. A comparison of the cuticles of different forms of Ptilophyllum pecten enabled Thomas to recognise more than one type: for one of these the name Ptilophyllum hirsutum is proposed. It is by such work as this that we may hope to discover differentiating characters.

The different forms of Williamsonia flowers found in association with fronds of the Ptilophyllum habit also point to the inclusion of more than a single species under the group-species P. pecten. As additional evidence is obtained further analysis will be possible, but in dealing with impressions which include specimens transitional from one form of frond to another, the most convenient and to my mind the most logical course is to treat a species as an aggregate- or group-species. Some authors believe that the two fronds described by Phillips as Cycadites pecten and C. pectinoides are distinct species[1463], but there would seem to be no adequate reason for this view. The fronds described by Heer[1464] from the Lower Cretaceous of Greenland as species of Zamites and similar leaves from Graham Land included in that genus by Halle[1465] are in my opinion inseparable from Ptilophyllum, and this applies equally to Otozamites Hislopi (Old.) (fig. 589) and O. abbreviatus as figured by Feistmantel and by Halle. The nomenclature of Cycadean fronds having the habit of Ptilophyllum pecten is a great difficulty: after carefully reconsidering the whole question and comparing Feistmantel’s figured specimens with the large series of English fronds the conclusion reached is that the characters exhibited by ordinary impressions do not admit of any satisfactory grouping under well-defined specific types. In the first place, as already indicated, the use by some authors of the generic names Ptilophyllum, Otozamites, and Zamites creates a false impression of the degree of difference between the numerous forms of frond agreeing more or less closely with the specimens on which were founded the species Ptilophyllum acutifolium, P. cutchense, P. pecten, and P. pectinoides (figs. 587, 591, 595, etc.). In his important memoir on the Jurassic flora of Graham Land Halle[1466] discusses the limitation of Ptilophyllum, Zamites, and Otozamites. He employs Zamites for fronds with linear pinnae attached to the upper face of the rachis by a base which is more or less, but often very little, rounded and always asymmetrical, with or without a basal callosity: fronds of the type Z. gigas he includes in the section Euzamites, while Z. borealis and similar forms (fig. 597) are referred to a second section, Subzamites. It is in the sense of Halle’s section Euzamites that the generic name Zamites is employed in this chapter. On the other hand the fronds grouped by Halle as Subzamites have pinnae with the basal angles of the lamina very slightly rounded precisely as in Ptilophyllum as seen in fig. 596 (cf. fig. 598 which represents fronds referred by Halle to Zamites); and they are not distinguished by any feature of generic importance from Ptilophyllum as defined on page 519. The species Zamites pusillus, Z. Anderssoni, and Z. antarcticus (fig. 598) described by Halle from Graham Land as well as Heer’s Arctic forms[1467] Z. borealis (fig. 597), Z. speciosus, Z. brevipennis, and others are transferred to Ptilophyllum as types agreeing very closely with P. pecten and in some cases not clearly distinguishable from it even specifically.

Otozamites is the name employed by Halle for fronds with pinnae having contracted, asymmetrical and auriculate, bases, the anterior lobe being more developed than the posterior. The asymmetry of the pinna-base is considered an essential feature. As Halle states it is very difficult in some instances to draw a distinction between Otozamites and Ptilophyllum. As used in this chapter Otozamites signifies fronds with pinnae characterised by an auriculate base, a lamina usually broader than in Ptilophyllum, and by more spreading veins (fig. 604). The not infrequent occurrence of auriculate pinnae on fronds (fig. 603, A) which cannot be separated from typical examples of P. pecten illustrates the narrow dividing line as regards the form of the pinna-base between Ptilophyllum and Otozamites. The Indian species O. Hislopi (fig. 589) and O. abbreviatus, to which Halle refers some Antarctic fronds, cannot be distinguished from the English P. pecten or Feistmantel’s and Morris’s Indian fronds described as P. cutchense and P. acutifolium: these forms are therefore included in Ptilophyllum.

Ptilophyllum (Williamsonia) pecten (Phillips).

This designation is employed in a wide sense for a group of fronds exhibiting a considerable range in size, in the relative breadth and length of the linear pinnae, and in other features. Under P. pecten are included (i) the English fronds from Yorkshire first described by Phillips[1468] as Cycadites pecten and C. pectinoides, the former from the Middle shale, the latter from the Lower shale of the Yorkshire coast, together with the Stonesfield slate specimens named by Sternberg[1469] Polypodiolites pectiniformis (fig. 595) and by Brongniart[1470] and Lindley and Hutton[1471] Zamia pectinata; (ii) the Indian specimens already considered and (iii) numerous examples recorded under different names from Jurassic strata in many countries. Fronds from the Yorkshire coast named by Brongniart[1472] Zamia Goldiei, though regarded by some authors as examples of Otozamites, are probably referable to P. pecten. Andrae’s Pterophyllum rigidum[1473] (fig. 596) from Steierdorf is almost certainly a form of Ptilophyllum pecten. The specimen shown in fig. 587 is one of the few examples of fronds apparently preserved in their original position attached in a cluster to a Williamsonia (Bucklandia) type of stem. The range in size and form of the pinnae is illustrated in figs. 588, 592, 593.

Fronds linear, tapering gradually towards the base and apex, often characterised by a marked uniformity in breadth. The pinnae, short or comparatively broad or long and narrow, are straight or more or less falcate; the apex is obtuse or acute or the upper margin of the lamina may be almost straight and the lower edge curved abruptly upwards at the apex; the pinnae are usually attached obliquely to the rachis but may be almost at right-angles; with the exception of the upper angle, the whole of the base is attached to the frond-axis; the base of the lamina may be symmetrical, both angles being slightly rounded, or asymmetrical, the upper or less frequently the lower corner being auriculate (figs. 592, 593). There is no basal callosity on the lamina nor is there a median sinus. The veins are more or less spreading at the base but for the most part parallel. The features of the epidermal cells and stomata are mentioned in the general account of the genus. Fertile shoots of plants with this type of frond are described under Williamsonia. Very little is known of the stems which bore Ptilophyllum fronds, but as stated on page 488 Indian specimens show leaves of Ptilophyllum cutchense attached to a piece of stem (fig. 579) having the characters of Bucklandia and characterised by a xylem-cylinder denser than in recent Cycads; the structure of the wood at least in the Indian stem is rather pycnoxylic than manoxylic.

The fronds grouped under Ptilophyllum pecten are very widely distributed in Jurassic floras; they are recorded from many localities in Europe, from Turkestan[1474], India, Graham Land[1475], Patagonia[1476], and elsewhere.

As thus defined this ‘species,’ or more correctly this group of forms, undoubtedly includes more than one species in the strict sense, but without additional data it is maintained that the recognition of clearly defined specific types or varieties is beyond our power. It may be urged that in view of the wide geographical range of the Ptilophyllum pecten type of frond and the admitted probability that several species in the narrower sense are represented, distinctive specific names should be retained even though under such designations are included forms that, so far as can be seen from impressions, exhibit no constant distinguishing features. My purpose is to emphasise the futility of attempting to found well-marked species on the available material. The student must decide for himself what course to pursue, whether to retain such a specific name as cutchense for the Indian fronds or to employ that and other specific names as designations of geographical types differing in no clearly defined or constant characters from examples of the English Ptilophyllum pecten. A comparative examination of the cuticular membranes in the comparatively few cases where that is possible would probably furnish a basis for a satisfactory subdivision of the group-species.

The names Ptilophyllum Anderssoni, P. boreale, and P. antarcticum are retained for certain forms selected from a number of closely allied types partly on the ground that these fronds exhibit some more or less well-marked distinctive characters and in part as a recognition of the existence of geographical forms.

Ptilophyllum boreale (Heer).

Heer[1477] described numerous well-preserved impressions of pinnate fronds from the Lower Cretaceous plant-beds of Kome, Greenland, which he referred to several species of Zamites though the differences between them are hardly of specific rank. An inspection of several of the figured specimens in the Stockholm Museum showed that Heer’s drawings are in the main accurate. Zamites borealis (fig. 597) is characterised by small linear pinnae attached to the upper face of the rachis, the stoutness of which is a noteworthy feature; the veins are parallel and simple. In the shape of the pinnae, including the base-characters, this species agrees closely with P. pecten. The slightly falcate or straight pinnae are 1·7–2 mm. broad and reach a length of 15 mm.; in Z. speciosum Heer, probably specifically identical with P. boreale, the pinnae are relatively longer, and in Z. brevipennis Heer they resemble the shorter pinnae of some of the narrow fronds of P. pecten.

A preparation of the cuticle of a pinna of P. boreale made by Mr Thomas from a specimen in the Stockholm Museum shows a marked difference between the upper and lower epidermis: the cells on the upper surface of the lamina have very thick and sinuous walls precisely as in P. pecten, but the cells are often broader than long and not elongated parallel to the long axis of the pinna; those of the lower epidermis are thinner and less clearly preserved: the stomata, which appear to be like those of P. pecten, are scattered and not in rows.