284 



NORTH-CAROLINA GEOLOGICAL SURVEY. 



ARCADAE. 



The valves in the Arcadae are equal, regular, and usually 

 oblique ; the teeth are arranged in long rows, resembling a 

 comb ; at the extremes they are longer and frequently curved 

 or corrugated. 



ARCA LIENOSA. SAY. (Fig. 204.) 



Shell large, inflated, oblique ; ribs subequal, numerous, 

 with a groove or channel in the middle ; anterior side angu- 



FIG. 204. 



lar ; lines of growth distinct, giving a striate appearance ; the 

 ligament area is marked by strong lines diverging from be 

 neath the umbo; umbones distant; inside margin strongly 

 sulcate or ribbed. It has about 37 ribs. A living shell upon 

 the Florida coast, but found abundantly in the miocene of 

 North-Carolina. 



A. SCALARIS. 



Shell oblong, ovate ; ribs twenty-one, strong and trans 

 versely rugose, ligament area short, transversely marked by 

 lines, and crossing striae parallel to the hinge line. 



A. INCILE. SAY. 



Shell very oblique, sub-quadrangular ; anterior side very 

 short, posterior sinuate ; ribs unequal, stronger on the poste 

 rior margin ; rounded before, angular behind, and much pro- 



