556 



CYCADOPHYTAN FRONDS 



[CH. 



Balli 1 , though superficially similar to Pterophyllum, appears to 

 agree more closely with Pseudoctenis. 



Pterophyllum Nathorsti Seward. 



This species, founded on a specimen in the Sedgwick Museum, 

 Cambridge, from the Middle Jurassic beds of Yorkshire, was 

 formerly referred to the genus Dioonites 2 , but since the Yorkshire 

 specimens were supplemented by material from Kimmeridge 

 strata in Scotland 3 affording more definite information with 

 regard to the attachment of the pinnae it has been transferred 

 to Pterophyllum. Pinnae laterally attached to the rachis which 

 in some specimens shows a transverse wrinkling, narrow, linear, 

 3 4 mm. wide and reaching a length of 9 cm. The base of the 



FIG. 614. A, B, Pterophyllum Nathorsti ; A from below; B from above. C, Nils- 

 sonia tenuicaulis. (A, B, Gunn Collection, British Museum; C, Arber Coll. 

 Sedgwick Museum, 539; nat. size.) 



segments is slightly expanded; the apex is acuminate or bluntly 

 pointed : there are approximately three veins in 1 mm. of lamina. 

 This type (fig. 614, A, B) is similar to Pterophyllum aequale Brongn. 

 as figured by Zeiller 4 from the Rhaetic of Tonkin and agrees 

 closely with some of the large Rhaetic specimens referred by 

 Schenk to P. Braunianum. The Jurassic fronds from Oregon 

 described by Fontaine 5 as Ctenophyllum angustifolium are similar 



1 Feistmantel (86) PI. n. A. figs. 48. 



2 Seward (00) B. p. 239. 3 Seward (II 2 ) p. 694, Pis. iv., v. etc. 

 4 Zeiller (03) B. PI. xix. 5 Fontaine in Ward (05) B. PL xxn. 



