18 AMERICAN COREICULAD^. 



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

 very narrow, rather straight. 



Fig. 12. 



C. olivacea. 



Long. 2.50; Lat. 2.06; Diam. 1.25 inches. 

 &quot; 63;- &quot; 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, PHILIPPI, Zeit. Malak. 1851, 70. DESK. Brit. 



Mus. Cat. 1854, 253. 

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



Philippi and Deshayes have both confounded this species with 

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

 shell with Yery regular strise and with an even epidermis 



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

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

 covering 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, subeqnilate- 

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

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

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



