MARINE MOLLUSOA OP THE UNITED STATES. 17*7 



Genus CHAMA, Linnseus. 

 Syst. Nat., edit. x. 1758. 



1. C. ARCINELLA, Linnaeus. Fig, 459, 462, 463. 



Syst. Nat., edit. xii. 1139. 1767. 



Shell heart-shaped, with a large depressed lunule beneath the 

 umbones, both valves radiately ribbed, the ribs spinous, and the 

 interstices punctured ; margins very finely crenulated. White or 

 yellowish, most frequently stained with pink-red. 



North Carolina to West Indies. 



The spines are generally only partially developed. 



2. C. MACROPHYLLA, Chemnitz. Fig. 460. 



Conch. Cab., vii. 149, t. 52, f. 514, 515. 1784. 



Shell ovate, both valves lamellated throughout, lamellae imbri- 

 cated, large, irregular, striated ; margins of the valves very 

 minutely crenulated; color bright yellow, whitish within. 



North Carolina to West Indies, 



Family ARCADE. 



Animal with the mantle open ; foot large, bent, and deeply 

 grooved ; gills very oblique, united posteriorly to a membranous 

 septum. 



Synopsis of Genera. 



Shell equivalve or nearly So, oval or subquadrate, ventricose, strongly ribbed 

 or cancellated; margins smooth or dentated, close or siuuated ventrally 

 hinge straight, teeth very numerous, transverse; umbones anterior, 

 separated by a flat, lozenge-shaped ligamental area, with numerous 

 cartilage-grooves. ARCA, Linn. 



Shell orbicular, nearly equilateral, smooth, or radiately striated ; umbones 

 central, divided by a striated ligamental area ; hinge with a semicircular 

 row of transverse teeth ; margins crenate within. 



PECTUNCULTJS, Lam. 



Shell trigonal, with the umbones turned towards the short posterior side ; 

 smooth or sculptured ; epidermis olive, interior pearly, margins crenu- 

 lated ; hinge with a prominent internal cartilage-pit, and a series of sharp 

 teeth on each side: NUCULA, Lam. 



Shell oblong, rounded in front, produced and pointed behind ; margin noj, 

 crenated : pallial line with a small sinus; teeth as in Nucula. 



LEDA, Schum. 



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