44 PLEIOCENE FOSSILS. 



ARCA iEQUICOSTATA.— Con. 



Plate XVL, Figs. 3 and 4. 



A. testa ovata, inflata : latere buccali brevi, rotundato ■ latere anali sub-elongato • costis 

 valvaz sinistralis rotundatis, latere anali crenulatis ; valvce dextralis, costis sub-planis ; denti- 

 bus cardinalibus numerosis ; area ligamenti sulcata, sublata ; umbonibus elevatis distantibus. 



Description. Shell ovate, inflated ; buccal side short, rounded ; anal side somewhat 

 elongated ; ribs of the left valve rounded, crenulated on the anal side ; ribs of the right 

 valve somewhat flat ; cardinal teeth numerous ; ligament area channelled, rather wide ; um- 

 bones elevated, distant. 



This is a pretty well marked species, that can only be confounded with A. improcera, 

 from which it is separated by its more rounded outline, greater size, and more produced 

 anal side. 



Plate XVI., Fig. 3. Exterior of left valve, hinge and teeth of right valve. 



" 4. End view of fossil, showing outline, hinge and umhones. 



Locality. Sumter Dist. 



Museum, College of Charleston. 



