2Q POST-PLEIO GENE FOSSILS. 



the beaks • ribs thirty-seven to thirty-nine, radiating, flat, and divided in the middle by a 

 lono-itudinal line, which becomes obsolete on the umbones ; margins strongly impressed 



within. 



This is a common species on the coast of North and South-Carolina, and Georgia ; it 

 has been lono- confounded with Arca pexata, (Say,) a shell limited in its Southern range 

 to Cape Hatteras; A. Americana, is readily distinguished from it by the truncated anal 

 maro-in ; the greater number of ribs, thirty-seven to thirty-nine, and less prominent 

 umbones ; the spaces between the ribs are deeper and narrower. 



Like A. pexata, {Say,) and A. holmesii, {Stimpson,) it has the hinge-line terminating 



at the beaks. 



Numerous and fine specimens are obtained from all the Post-Pleiocene beds of the 



State. 



Plate IV. Fig. 2, Exterior, and hinge. 

 " 2a, Etid view. 



Locality. Charleston; Simmons'. 



Museum, College of Charleston; Cabinet F. S. H. 



ARCA LIENOSA. 



Plate IV. Figs. 3 and 3a. 



Area lienosa, Saij, Am. Conch., pi. 36. 



Arca lienosa, Tuomey Sf Holmes, Pleiocene Foss. So. Ca., p. 40, pi. 15, fig. 2. 



Arca lienosa, Say's Conch. U. S., (Binney,) p. 192. 



Description. Shell equilateral, transversely oblong, inflated, ribbed, rugose; buccal 

 side produced, angular ; anal side elongated, obliquely truncated ; ribs about thirty-five, 

 unequal, channelled; ligament area, wide, sulcate; sulci slightly diverging, but somewhat 

 parallel to the hinge ; umbones distant. 



We are not aware of this species now existing, except upon the coast of Florida ; it is 

 rare in the Post-Pleiocene, but more abundant in the Pleiocene of South-Carolina. 



Plate IV. Fig. 3, Shell, natural size. 

 " 3rt, Vietv of hinge. 



Locality. Simmons'. Museum, College of Charleston ; Cahiriet F. S. H. 



