46 PLEIOCENE FOSSILS. 



ARCA PEXATA.— Sat. 



Plate XYL, Figs. 7 and 8. 



A. testa suborbiculari ; lateribus rotundatis ; latere buccali breviore ; radiatim costata; costis 

 medio sulco exile divisis ; area ligamenti angustissima ; umbonibus fere inter se contingentibus. 



Description. Shell somewhat orbicular, sides rounded; buccal side the shorter; ribs 

 divided in the middle by a groove ; ligament area very narrow ; umbones nearly touching. 



With the exception of A. Americana, Gray, and A. Holmeseii, Kurtz and Stimson, this 

 is the only species having the hinge line terminating at the umbones. Only a single valve 

 of this shell, so common an inhabitant of our coast, has been found fossil, and even this is 

 not a very characteristic specimen, as it is somewhat distorted, having undergone repairs 

 by the animal. We, therefore, give the figure of a recent specimen. 



Plate XVI., Fig. 7. Exterior of left valve, hinge and teeth of right valve. 

 " 8. End view, showing hinge and umbones. 



Localitt. Darlington District. 



Museum, College of Charleston. 



