170 AMERICAN JOURNAL 



DESCRIPTION OP NEW SPECIES OF MARINE BIVALVE 

 MOLLUSCA IN THE COLLECTION OF THE ACADEMY OF 

 NATURAL SCIENCES. 



BY GEORGE W. TRYON, JR. 



PHOLADID^. 



1. Cyrtopleura exilis, Tryon. — Plate 14, fig. 2. 



Description. — Shell long and narrow, covered with numerous 

 scabrous radiating ribs, except a narrow surface parallel with 

 the posterior dorsal margin which is smooth. Widely gaping 

 anteriorly, acuminate posteriorly. Dorsal lamina ? 



Length 10, width 30 mill. 



Sab. — Ins. St. Croix, West Indies. 



Remarks. — This species, collected and presented to the Acad- 

 emy by the late Dr. R. E. GriflSth, has heretofore been con- 

 founded in our collection with O. crueigera, Sowerby, a Panama 

 species ; it is, however, smaller and narrower, and belongs, it 

 will be perceived, to a different fauna. 



MACTRID^. 



2. Mactra Gabbi, Tryon.— Plate 16, fig. 7. 



Description. — Shell oval, nearly equilateral, thin, depressed, 

 beaks narrow, not prominent, with a slight raised line radiating 

 to the margin, smooth, light corneous. 



Length 31, width 40 mill. 



Hah. — Lower California. Wm. M. Gabb. 



Remarhs. — This species I cannot approximate closely to any 

 other in the genus ; its equilateral regularly oval form, small 

 umboes and thin texture will serve to distinguish it. Two speci- 

 mens are in our collection. 



