﻿92 PROF. A. c. SEWARD ON [Feb. 1 908^ 



to fronds either simple or branched, which in habit and in the 

 form of the ultimate segments agree very closely with Thinnfeldia. 

 Prof. I*Tathorst's species from the Rhsetic of Scania and Prof. Keillor's 

 specimens from Tongking may suffice as examples. It would seem 

 that the chief distinguishing feature between these fronds and those 

 of Thinnfeldia is in the venation. In Ptilozamites and Ctenopteris^ 

 the pinnules are without a midrib, and the simple or forked veins 

 are all direct branches from the axis of the pinna or rachis ; this 

 type of venation is represented in pinnules of Ptilozamites reproduced 

 from Nathorst^ in fig. 3E (p. 91). We have seen that a pinnule of 

 Thinnfeldia may also exhibit the same form of venation (figs. 3 A 

 & 3D) ; but, as a rule, the veins are found to curve downwards at 

 the base of the lamina before coming into contact with the axis of 

 the pinna (fig. 3 B). As our knowledge of the fructification ^ of the 

 genera that have been mentioned is very incomplete or almost nil^ 

 we must rely on vegetative characters for distinguishing marks ; and 

 it is necessary to decide how far these supply criteria for generic 

 distinctions. Granting that, in many cases, the venation of the 

 ultimate segments furnishes a means of separating Thinnfeldia from 

 Ctenopteris and Ptilozamites, it is more than doubtful whether these 

 differences, which are not constant, can be accepted as of generic 

 rank. Without attempting a revision of the various species referred 

 to the genera Ptilozamites, Ctenopteris, Cycadopteris, and Thinnfeldia, 

 I would express the opinion that Ctenopteris Sarrani of Zeiller ^ is 

 not generically distinct from Thinnfeldia odontopteroides as figured 

 by Feistmantel and other authors from Australia and elsewhere. 



Thinnfeldia odontopteroides (Morris). (PI. lY, fig. 1 & PL V, 

 fig. 1.) 



The variable character of this species as regards the size and 

 shape of the segments and their venation, alluded to in my former 

 paper on African plants and pointed out by other writers/ renders the 

 task of delimiting species almost hopeless when we have to trust to 

 fragments of sterile pinnae. Some of the examples of Thinnfeldia- 

 included in the collection submitted to me are unquestionably 

 specifically identical with specimens already figured from South 

 Africa, while others (text-fig. 3 & PI. Y, fig. 1) are characterized 

 by broader leaflets and arc clearly identical with the larger fronds 

 described by Peistmantel^ from the Hawkesbury Series of New 

 South Wales. It is possible that more than one species is repre- 

 sented, but the occurrence of intermediate forms favours the use of 

 the designation Th. odontopteroides in a comprehensive sense. 



I would, however, point out that it is not improbable that under 

 the designation TJi. odontopteroides more than one specific type is 

 included. While recognizing this possibility, I do not at present 



1 Nathorst (78) pi. xii, figs. \h k\c {Ptilozamites Heeri, Nath.). 



•^ Kaciborski (94) p. 206 & pi. xx, figs. 1-2 ; Zeiller (00) p. 97. 



■■* Zeiller (02) p. 53 & pis. vi-viii. 



-I Feistmantel (90) p. 104; Shirley (98) p, 21. ^ Feistmantel (90) pi. xxiv. 



