PLATE XIX. 



Fig. 



6. Strophalosia Gerardi, King. Small valve, &c.j (natural size) of a testiferous 



specimen : «, area of large valve^ with its deltidium or 

 closed fissure (^) ; c, area of small valve. 

 (This specimen was collected by the late Dr. Gerard in crossing 

 the boundary of Ladakh and Bis-ahar in the Himalayas, at an 

 elevation of 17,000 feet above the level of the sea). 



7. — — Large valve of the last specimen. 



8. Trigonia margaritacea, Lamarck. Enlarged view of the dental system for the 



purpose of comparing it with its homologue in Schi- 

 sodus truncatm. 



A, Left valve. 



B, Right valve. 



a. Ridge fitting into the groove, a* 

 h. Groove for the ridge, h* 



c, Cleft tooth fitting into the triangular opening, c* 



d, Groove for the ridge, d* 



e, Ridge fitting into the groove, e* 

 /, Cardinal muscular fulcra. 



