42 DESCRIPTION OF NEW 



Margaritana Holstonia. Plate XIII. fig. 37. 



Testa subarcuata, suhinflata, transversa, valde incBquilaterali ; ad latus jjlannlata; val- 

 vulis subtenuibus ; natibus subprominulis, undulatis ; epidermide fusca ; dentibus cardinali- 

 bus magnis; margarita alba et iridescente. 



Shell subarcuate, somewhat inflated, transverse, very inequilateral, flattened on the 

 side; valves rather thin; beaks somewhat prominent, undulated; epidermis brown; 

 cardinal teeth large ; nacre while and iridescent. 



Hab. Holston River. Professor Troost. 



Cabinet of Professor Troost. 

 Diam. -8, Length 1-2, Breadth 2-4 inches. 



Shell subarcuate, somewhat inflated, transverse, very inequilateral, 

 flattened on the side, rounded on the umbonial slope ; valves rather 

 thin, thicker before ; beaks somewhat prominent, irregularly and finely 

 undulated at the tip; ligament rather long; epidermis brown, wrin- 

 kled, and apparently without rays ; cardinal teeth large, and elevated 

 into three points in the left valve, smaller in the right valve, and ele- 

 vated into a single point; anterior cicatrices confluent; posterior cica- 

 trices confluent ; dorsal cicatrices placed on the inferior portion of the 

 cardinal teeth ; cavity of the shell rather deep ; cavity of the beak 

 shallow and angular ; nacre white and iridescent. 



Bemarks.— This species is the production of Holston River, but I am 

 not aware from what part it was procured by Professor Troost, to 

 whose kindness I owe the privilege of describing it. It is more nearly 

 allied to the M. Raveneliana (nobis) than any other species of this genus. 

 It may be distinguished from it by its being more compressed, in the 

 form of its teeth, and in being without rays. The last character must, 

 however, be received with some doubt, as specimens may be found with 

 rays. The single specimen before me having no rays, does not prohi- 

 bit their occurrence in others. The teeth of the left valve are re- 

 markable in being elevated into three distinct points, the two posterior 

 ones clasping into the cavity of the beak of the other valve. 



