536 



PTERIDOSPERMS, ETC. 



[CH. 



The main rachis gives off branches as in Mariopteris, but in 

 Diplotmema each naked lateral branch is forked at its apex 

 into two opposite pinnae bearing deeply dissected Sphenopteroid 

 pinnules. Zeiller' and Stur have recorded fertile specimens 

 of Diplotmema, but in no case have actual sporangia been 



h^ 



Fio. 355. A. Cephalotheca mirabilis, Nath. Fertile pinnae. (Partially re- 

 stored. After Nathorst.) 

 B. C. mirabilis. Sterile pinnule. Nat. size. (After Nathorst.) 



discovered. In the species Diplotmema Zeilleri Stur (fig. 354, 

 C, C) two Aphlebiae occur at the base of each secondary axis'-. 

 It has been pointed out by Potonie that in Diplotmema furcatum 

 the equal dichotomy of the lateral branches is not characteristic 



' Zeiller (88) A. p. 147. 



" Ibid. PI. XVI. 



