322 



TRIGONOCARPALES 



[CH. 



in transverse section, each angle being prolonged as a narrow 

 flange. In one of the sections figured by Brongniart (fig. 495, E) 

 the ribs are not fissured : this is said to be a feature distinguishing 

 Hexapterospermum from Ptychotesta, but the occurrence of a 

 fissured rib in another section suggests that in the structure of 



B^G. 495. A, Polypteroapermum BenauUii. B, Ptychotesta tenuis. C, D, Poly 

 lophospermum stephanense; sa, sarcotesta; s, spaces; v, vascular bundles. 

 E, Hexapterospermum stenopterum. F, Diplotesta avellana. G, Taxospermum 

 Griineri. H, Diplotesta Orand' Buryana. (After Brongniart ; C, after Oliver. ) 



the ribs there is no essential difference between the two genera. 

 In Ptychotesta pachypterum the testa is prolonged at the chalazal 

 end as in Polylophospermum, and it is possible that there is no 

 generic difference. Wilhamson described a cast from the Coal 

 Measures of Lancashire as Hexapterospermum [= Hexagonocarpus] 

 Noegerraihi'^ (fig. 506, H), but in the absence of anatomical 

 characters it is preferable to avoid the use of Brongniart's term 

 and to assign them to Renault's genus Hexagonocarpus^. Similarly 

 1 Williamson (77) B. p. 253. ^ gee page 356. 



