12 CYCADACEJE. 



this species, the same authors institute five other specific names 1 

 for isolated pinme which do not appear to afford any distinct 

 indication of specific difference. Potonie, 2 in his recent work on 

 the Permian flora of Thuringen, includes all these five species 

 under Zamites carbonarius, and an examination of the figured 

 pinna3 certainly lends support to this view. Zeiller 3 has defended 

 Eenault's determination, on the ground that there are certain 

 differences in the venation and form of the pinnae which are 

 hardly consistent with the suggested inclusion under a single 

 species ; he is, however, willing to admit that possibly Zamites 

 reyularis may he identical with Z. Planchardi. Whatever may be 

 the specific value of these Commentry specimens, Zeiller regards 

 them as undoubtedly fragments of the same generic form, and the 

 discovery of more perfect specimens leads him to found a new 

 genus, Plagiozamites, as more suitable for their reception than 

 Zamites. In speaking of the resemblance between Plagiozamites 

 and Noeggerathia, Zeiller expresses an opinion in favour of 

 including the latter genus among cycads, using the term cycads 4 

 in a wide sense. This opinion is partly based on the close 

 similarity between Noeggerathia and Plagiozamites on the one 

 hand, and on the marked resemblance between the latter genus 

 and Zamites on the other. The form of the fronds certainly 

 favours this view, but such reasoning from external resemblance 

 cannot be accepted as conclusive when we are dealing with cycads 

 and ferns. In all these cases we must be prepared to find a 

 combination of pteridophytic and cycadean characters, and if we 

 were in possession of the facts of anatomical structure, we should 

 possibly be quite unable to decide definitely for one or other of 

 these two groups of plants. 



The Commentry flora has furnished an exceedingly fine specimen 

 of the genus Pterophyllum* P. Fayoli, Ren. and Zeill. This 

 example is unusually large and well preserved, and there can be 

 little or no hesitation in accepting it as a Palseozoic cycadean 

 frond, having an equally strong claim to be described as such as 



1 Flor. Commentry, pp. 615-617, pi. Ixvii. figs. 8-19. 

 ~ (1), P- 210. 



3 (2), p. 177. 



4 Ibid. p. 179. 



6 Renault and Zeiller (2), p. 619, pi. Ixviii. fig. 1. 



