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.)