32 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I48 



have "lateral buttress plates" to the spondylium (Stepanov, 1937), 

 but internal structures of the Permian genus Torynechus Cooper and 

 Grant are exactly like those of Stenoscisma. 



Torynechus probably descended from Stenoscisma by reduction of 

 the stolidium to a marginal ridge, thickening to an uncinuliform shape, 

 and by development of finer, more numerous costae. Septacamera lacks 

 any trace of the stolidium, and is assigned to the Torynechinae mainly 

 on the basis of an external shape like Torynechus and costation that 

 recalls some species of Stenoscisma. 



