436 NEW GENUS AND SOME NEW SPECIES 



Cabinet of T. G. Lea. 

 Cabinet of Prof. Vanuxem. 

 Cabinet of P. H. Nicklin. 

 Cabinet of the Academy of Natural Sciences. 

 Cabinet of Peale's Museum. 

 Diam. 1-6, Length 2-3, Breadth 3-4 inches. 



Shell ovate, inequilateral, sub-elliptical, transverse, very 

 ventricose ; substance of the shell somewhat thick ; beaks 

 large, prominent, rounded, approaching, slightly undulated, 

 rarely decorticated; ligament short and thick; epidermis 

 slightly wrinkled, shining, olive yellow, with green rays pas- 

 sing obliquely from the beaks to the margin, most numerous 

 on the posterior slope ; cardinal teeth double and very promi- 

 nent in both valves ; in the left valve the cleft is deep and 

 both prongs rake much, the outer most elevated ; in the right 

 valve the cleft is also deep, and the inner prong is broad, flat, 

 curved, and most elevated ; lateral teeth short and very lamel- 

 liform, the termination declining rather suddenly ; anterior 

 cicatrices generally distinct; posterior cicatrices confluent; 

 dorsal cicatrices very perceptible, the line commencing with 

 quite a large one on the under side of the callus between 

 the lateral and cardinal teeth, and terminating at the outer 

 part of the base of the cardinal tooth ; marginal cicatrix very 

 perceptible ; cavity of the beaks deep, large and rounded ; 

 nacre milk white, rarely iridescent. 



Remarks. — The specimen figured is the finest I have ever 

 seen of this species, and, taking it altogether, perhaps of any 

 other of the genus. The rays are very remarkably fine, and the 

 nacre is purer and whiter than the finest porcelain. It is very 

 frequently, however, found with few or no rays, and the na- 

 cre, though milk-white and pure generally, is not always so. 

 The double, deeply cleft, cardinal tooth of both valves, and 

 the raking position of that of the left valve are peculiar to the 

 species possessing this general form, which includes the ova- 

 tus and ventricosus. It seems to form the link between these 

 two. It differs from the ovatus in not possessing the flat 



