THE FOSSIL OSMUNDACE^E. 471 



following Zygopteridese have only one row of "pinnse" on each side of the 

 main rachis : 



Zygopteris bibractensis, Renault — Will. 



Zygopteris corrugata, Will.* 



Zygopteris Williamsoni, P. Bertrand. 



Clepsydropsis antiqua, Unger. 

 This group, in fact, coincides with Bertrand's genera Ankyropteris and Clepsy- 

 dropsis. 



The pinna-trace departs as a closed ring in all of them, and the island extends along 

 practically the whole length of the arms, except in Clepsydropsis, where the arms may 

 be supposed to be undeveloped, as in our hypothetical primitive trace (text fig. 6). 



The Zygopteridese with two rows of " pinnae " on each side of the main rachis may 

 be subdivided according to the relative extension of their parenchyma islands. In the 

 first division the island extends the whole length of the arms, and the pinna-trace is 

 probably always given off as a continuous band almost as long as the whole length of 

 the arms (text figs. 10 and 11). 



Zygopteris Eomeri, Solms. 



Zygopteris forensis, Eenault, sp. 



Zygopteris primaria, Cotta. 



Zygopteris duplex, Will. 

 This division includes Bertrand's genera Metaclepsydropsis, Diplolabis, and 

 Zygopteris (Z. primaria). 



In the second division the island hardly extends beyond the lateral termination of 

 the cross-bar, and the pinna-trace is usually already double at or very near its point of 

 origin (text figs. 12 and 13). 



Zygopteris Lacattei, Eenault. 



Zygopteris Scotti, P. Bertrand. 



Zygopteris di-upsilon, Will. ( = Z. Grayi). 



Zygopteris tubicaulis, Goppert. 



? Zygopteris scandens, Stenzel. 

 This division forms Bertrand's genus Etapteris. 



The interesting genus Dineuron (text fig. 14) also belongs to this group; but, 

 since the arms are not developed, it cannot be assigned to one of the subdivisions more 

 than to the other. In fact, Dineuron bears the same relation to the second group as a 

 whole that Clepsydropsis does to the first group. That a Dineuroid type of trace 

 really is primitive in the second group is rendered very probable by Mr Gordon's 



* The vascular strands that we have observed to be given off from the free petiole of Zygopteris corrugata are all so 

 small thai they can hardly have supplied appendages of more importance than mere scales. Dr Scott figures the 

 insertion of such a scale near the base of a petiole, and compares it with an " aphlebia " (Studies in Fossil Botany, p. 313). 

 All the departures that we have seen suggest the same sort of thing. In fact, the occurrence of a fully developed 

 pinna-trace equivalent to that of Zygopteris bibractensis has not yet been described in Zygopteris corrugata ; indeed, it is 

 possible that none such existed. 



TRANS. ROY. SOC. EDIN., VOL. XLVII. PART III. (NO. 17). 70 



