PLATE XIX. 
Fig. 
6. Strophalosia Gerardi, King. Small valve, &c., (natural size) of a testiferous 
specimen: @, area of large valve, with its deltidium or 
closed fissure (4); ¢, 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). 
ic — —* 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- 
zodus truncatus. 
A, Left valve. 
B, Right valve. 
a, Ridge fitting into the groove, a* 
6, Groove for the ridge, 6* 
c, Cleft tooth fitting ito the triangular opening, c* 
d, Groove for the ridge, d* 
e, Ridge fitting into the groove, e* 
J, Cardinal muscular fulcra. 
