18 



AMERICAN CORBICL'LAD.E. 



anterior lateral tooth quite prominent, posterior shorter than usual ; sinus 

 very narrow, rather straight. 



C olivacea. 



Long. 2.50; Lat. 2.06; Diam. 1.2.5 inches. 

 " 63 ; " 52 ; " 32 mill. 



Hab. North America, at Mazatlan, in Mexico. (Cabinets of the British 

 Museum, Smithsonian Institution, State of New York, Cuming and Prime.) 



Cyrena fontaineii, Piiilippi, Zeit. Malak. 1851, 70. — Desh. Brit. 



Miis. Cat. 1854, 253. 

 Cyrena olivacea, Carp. Mazatlan Shells, 1857, 114. 



PMlippi and Deshayes have both confounded this species with« 

 the C. fontaineii of D'Orbigny, which is a more regularly formed 

 shell with very regular strife and with an even epidermis. 



Mr. Carpenter, in speaking of the G. olivacea, says it is known 

 outwardly by its flattened form, by its rich olive-green epidermis 

 c'ov(!ring the umbos and rising into irregularly corrugated folds, 

 which are very close on the anterior part. The interior displays 

 a very dark purple over the greater part of the surface. The out- 

 line varies considerably. So far this species has not been found 

 in any abundance. 



11. Cyrena regalis, Prime. — Shell small, subtrigonal, suheqnilate- 

 ral, somewhat compressed, transversely short ; anterior side rounded, 

 posterior side forming a declivity from the heaks, somewhat produced, 

 subabrupt at extremity ; beaks nearly central, small, not much raised, 



