BIVALVES. CHAMA. 57 



The American, Indian, and Atlantic Oceans ; and the 

 Mediterranean, Caspian, and Adriatic Seas, produce infi- 

 nite varieties of this genus. 



CHAMA Clam. 



DIVISION I. SHELL EQUIVALVE. 



FAMILY 1. With longitudinal ribs, gaping at the posterior slope. 

 Gigas Giant. Hippopus Spotted. 



FAMILY 2. With longitudinal ribs, posterior slope closed. 

 Antiquata Antiquated. Calyculata Variegated. 



Ajar Ajar. Pectunculus Peduncle. 



Trapezia Trapeziform, Satiata Obsolete. 



Rosea Rose-coloured. Rugosa Rugged. 



FAMILY 3. Shell longitudinally ribbed, having an ovate 



chamber in the interior of each valve. 



Concamerata Chambered. 



FAMILY 4. Shell decussated, or transversely striated, without 



ribs. 



Semiorbiculata Brown. Oblonga Oblong. 



Cordata Heart-shaped. Coralliophaga Coral. 



FAMILY 5. Shell tuberculated. 

 Plumbea Leaden. 



FAMILY 6. Heart-shaped, umbones prominent, and apices 



spirally recurved. 

 *Cor Heart. Moltkiana Moltkian's. 



DIVISION II. SHELL INEQUIVALVE. 



Lazarus Lazarus. Lamellosa Lamellar. 



Gryphoides Gryphus. Punctata Dotted. 



Cornuta Horned. Sinistrorsa Reversed. 



Sessilis Scaly. Arcinella Hedge-Hog. 



Ponderosa Heavy. 



D3 



