MYA. 219 
alata, shell moderately thick, subtriangular, gen- 
erally gaping at the back part of the base, fus- 
cous, wrinkled; beaks near the back part, de- 
corticated ; base straitish ; hinge-margin ob- 
lique with a winged process ; red-purple with- 
in; teeth crenate. Dimensions five inches and 
a half by three and three fourths. 
cylindrica, shell very thick, subcylindric, emargi- 
nate forward ; pale horn-coloured and greenish ; 
hinge-margin undulated obliquely across the 
wrinkles ; rough on each side; beaks broad 
and prominent 3; pearly within; teeth thick and 
crenate ; cavity of the beaks very deep. Di- 
mensions three inches and a quarter by one and 
a quarter. 
undulata, shell subrhombic, with undulations, which. 
radiate from the beaks; shell thick, obtusely 
rounded behind ; hinge-margin somewhat wing- 
ed 3 epidermis blackish. 
plieata, shell subquadrangular, tumid, sinuous 
before with distant oblique folds 5; hinge-mar- 
gin elevated, compressed, keeled ; shell thick. 
undata, shell subiriangular, very tumid, unda- 
lated ; lateral teeth two in each valve; shelk 
thick, beaks projecting backwards ; epidermis 
horn-colour approaching yeliowish-green ; teeth 
deeply furrowed and crenate, lateral teeth two 
in each valve. 
clipticea, regularly oval, thick, convex, glabrous ; 
beaks depressed ; teeth elevated, triangular, 
striated ; shell long befere and short behind ; 
epidermis yellowish-brown, obscurely rayed : 
teeth deeply divided, finely striated ; pearly 
white, iridescent or flesh-colour within. Di- 
mensions about four inches by two and a half. 
