MARINE MOLLUSCA OF THE UNITED STATES. LTT 
Genus CHAMA, Linnzus. 
Syst. Nat., edit. x. 1758. 
1. C. ARCINELLA, Linneus. Fig. 459, 462, 463. 
Syst. Nat., edit. xii. 11389. 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, £ 514, 515. 1784. 
Shell ovate, both valves lamellated throughout, lamellae imbri- 
eated, large, irregular, striated; margins of the valves very 
minutely crenulated; color bright yellow, whitish within. 
North Carolina to West Indies. 
Family ARCADA. 
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 sinuated 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. 
Prctuncutts, Lam. 
Shell trigonal, with the umbones turned towards the short posterior side ; 
smooth or sculptured; epidermis olive, intertor pearly, margins crenu- 
lated ; hinge with a prominent internal cartilage-pit, and a series of sharp 
teeth on each side. Nucuta, Lam. 
Shell oblong, rounded in front, produced and pointed behind ; margin not 
crenated ; pallial line with a small sinus; teeth as in Nucula. 
Lepa, Schum. 
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