PLEIOCENE FOSSILS. 39 



ARCA RUSTICA.— {New Species.) 



Plate XV., Fig. 1. 



A. testa crassa, sub-quadrata, radiatim costata ; costis sub-squamosis ; latere buccali brevi- 

 oribus, costis crenatis ; latere anali carinato, angulato, truncate, costis majoribus / umbonibus 

 inter sefere contingentibus. 



Description. Shell thick, somewhat square, radiately, and unequally ribbed ; ribs almost 

 squamose ; buccal side very short, ribs crenate ; anal side carinate, angular, truncate, ribs 

 very large ; ligament area narrow, umbones nearly touching. 



This fossil is readily distinguished by the coarse ribs and deeply excavated interstices on 

 the anal side. The margin is strongly crenulated. Only a single perfect valve has been 

 found, with a fragment of a larger individual, which is presented in Fig. 1. 



Plate XV., Fig. 1. Fragment of the only specimen in our possession. The outline is correct. A 

 perfect shell, though much smaller, was lost after the outline of Fig. 1 had 

 been taken. 



Locality. Waccamaw. 



Museum, College of Charleston. 

 11 



