226 NTLSSONIA. 



39,292. PI. IV. Fig. 5. 



A frond 28 cm. long and 6-2 cm. broad at the widest part ; 

 labelled by Bean Pterophyllum comptum. This unusually good 

 specimen demonstrates the Nilssonia character of the species, the 

 typical form of the segments, and the general habit of the frond. 

 The parallel veins are well marked as prominent ridges on the 

 surface of the segments. 



Gristhorpe Bay. Sean Coll. 



V. 2894. Text-figs. 39A and B. 



Good examples of fronds of medium width. In one of the 

 specimens (Fig. A) the manner of attachment and form of the basal 

 segments are clearly shown ; they extend to the middle of the 

 upper face of the rachis, and are not attached to the edge as in 

 Pterophyllum. In Fig. B the basal segments are much shorter 

 and smaller than in the example illustrated in Fig. A. These two 

 figures afford good examples of the variation in the basal portion 

 of fronds of the same species. The longest frond measures 18cm. 

 in length. 



Near Scarborough. Beckles Coll. 



40,469. Text-fig. 39c. 



Another basal portion of a frond, showing the broad petiole 

 and the form of the lowest segments. The segments of this 

 frond have very prominent veins as broad ribs, with occasionally 

 much finer veins between. The prominence of the ribs is no 

 doubt due to the presence of bands of thick-walled hypoderm, 

 which with the vascular bundles probably constituted I -shaped 

 strengthening .girders stretching across the lamina. 



Text-fig. 40. 



Part of an unusually large frond in the Whitby Museum. 

 Owing to the imperfect state of preservation of the median 

 portion, the segments do not extend so far over the upper face 

 of the rachis as in the more perfect specimens. The whole frond 

 measures more than 40 cm. in length, and has a breadth of 9 cm. 

 Cf. Schenk's figures of Nilssonia polymorpha ; also the fronds from 

 India described by Oldham & Morris as Pterophyllum prmceps. 



