- Lomatopteris jurensis. (⅞ nat. size. After Kurr.)
- L. Schimperi. (⅞ nat. size. After Salfeld.)
- Thinnfeldia rhomboidalis, Ett. (Slightly enlarged. British Museum. No. 52672.)
Lomatopteris.
The generic name Lomatopteris was proposed by Schimper[1450] for some bipinnate fronds originally described by Kurr[1451] from Jurassic rocks of Württemberg as Odontopteris (?) jurensis ([fig. 360], A). I have elsewhere expressed the opinion[1452] that this German species may be identical with Thinnfeldia rhomboidalis Ett. Kurr’s type-specimen, a portion of which is reproduced in [fig. 360], A, consists of a frond or large pinna characterised by a prominent and broad rachis giving off alternate linear pinnae bearing bluntly rounded, contiguous and basally concrescent pinnules having a thick or revolute border and a central rib. The lateral veins are visible in the ultimate segments of Kurr’s fossil. Saporta[1453] has described several species, which he refers to Schimper’s genus, from French Jurassic strata: it is, however, difficult to recognise some of the examples represented in his illustrations as specifically distinct forms. This author notices the resemblance of Lomatopteris to Thinnfeldia, not only in habit but in the structure of the epidermal cells[1454]. In Lomatopteris and in Thinnfeldia the cells have straight and not sinuous walls and the slightly sunken stomata are surrounded by a ring of epidermal cells. Salfeld[1455] has recently described portions of fronds from Jurassic rocks of South-West Germany, which he identifies as Lomatopteris jurensis. He disagrees with my view that Lomatopteris does not differ sufficiently from Thinnfeldia to be accorded generic autonomy, chiefly on the ground that the folded-over edge of the pinnules is a distinguishing feature of Lomatopteris. There is, however, no difference, in appearance at least, between the leaflets of some species of Thinnfeldia, e.g. T. rhomboidalis from Liassic rocks of England[1456], and those referred to Lomatopteris. In a later paper, Salfeld[1457] describes some Portlandian fragments from North Germany as Lomatopteris Schimperi, identifying them with a Wealden fossil of somewhat doubtful affinity, which Schenk[1458] makes the type of his species. The Portlandian specimens are described as tripinnate, with thick decurrent obtusely terminated pinnules with a revolute edge. The general form of the frond is very similar to that of L. jurensis. Salfeld publishes a photograph of a large specimen which he describes as fertile and a drawing of a piece of a pinna: the latter is reproduced in [fig. 360], B. He speaks of sori occurring in two rows, probably attached to lateral veins, in the groove between the midrib and the revolute edge of the lamina. The sporangia are described as “nicht näher bekannt[1459].” An examination of the figures reveals nothing as to the nature of the “sori.” The specimens are considered by Salfeld to afford decisive evidence against the view that Lomatopteris and Thinnfeldia are generically identical. Nothing has so far been published which constitutes a valid argument in favour of retaining Schimper’s generic name.
Cycadopteris.
Zigno[1460] founded the genus Cycadopteris on Italian Jurassic impressions regarded by Schimper as indistinguishable from Lomatopteris. As Solms-Laubach[1461] points out, the supposed sori of Cycadopteris described by Zigno are not convincing. There appear to be no satisfactory reasons for separating Cycadopteris from Lomatopteris, nor do the fronds described under these names exhibit any important differences from Thinnfeldia.
Ptilozamites.
Nathorst[1462] founded this genus on a remarkable series of specimens from the Rhaetic Coal-beds of Scania and assigned it to the Cycadophyta. The species Ptilozamites Heeri may be taken as a representative type. The leaves are linear and simply pinnate. In the example shown on a much reduced scale in [fig. 361] the frond is 53 cm. long and 2·1 cm. broad. The upper edge of each pinnule is straight or slightly concave; the lower edge is rounded; the veins are slightly divergent and dichotomously branched ([fig. 356], E, p. 539). In some of Nathorst’s specimens the broad rachis is forked as in many Thinnfeldias.
As a comparison of [fig. 356], A and E, shows, the pinnules of some specimens of Thinnfeldia odontopteroides are identical with those of Ptilozamites. In the latter genus the rachis is either unbranched or occasionally forked, while in Thinnfeldia the branching may be of the dichotomous or pinnate type. In Ptilozamites the segments appear to be always without a midrib, while a median vein frequently occurs in those of Thinnfeldia. There can be little doubt as to the very close alliance between the Rhaetic species referred to these two genera. The name Ptilozamites should perhaps be retained for such long and narrow fronds as that shown in [fig. 361]: no species included in Thinnfeldia is known in which the rachis reached so great a length without branching. The habit of Ptilozamites Heeri predisposes one in favour of Nathorst’s opinion that the fronds are Cycadean: we have no information in regard to the nature of the reproductive organs.
Fig. 361. Ptilozamites Heeri, Nath. (⅓ nat. size. After Nathorst.)