222 ; MY As 
cellate, white within ; epidermis yellowish- 
green, rayed with dark-green, finely striate 
transversely. Dimensions three fourths of an 
inch by an inch and a quarter. 
gracilis, shell triangular-ovate, very thin and fra- 
gile, hinge-margin elevated into a wing ; valves 
connate 3 ligument concealed ; epidermis sea- 
green, obscurely radiated ; bluish-white within 
and tinged with violet. Dimensions two inches 
- and a half by four. 
arvu, shell oblong-ovate, small, convex, sides 
rounded; beaks slightly elev ated s pearly-white 
and iridescent within ; epidermis brownish ; 
very brilliant within. Dimensions one inch by 
two thirds of an inch. 
Section C. Hinge with prominent cardinal teeth, 
but without lateral ones ; posterior cicatrice 
compound. ALAsMoDoNTA of Say. 
arciata, shell ovate, elongated transversely, thick ; 
base arched, ligament elevated, beaks depressed. 
cicatrices rough 5; epidermis brownish-black ; 
‘surface smooth in the young state, eroded and 
sczbrous when old ; teeth two in the right and 
one in the left valve; bluish-white within. Di- 
mensions two inches by four. 
vugosa, shell oblong-oval, anterior side with deep 
diverging folds ; epidermis chesnut-brown with 
a silky lustre ; surface of the fore part folded 
in a pinnate form ; cicatrices smooth ; pale flesh- 
colour in the center within, pearl white on the 
margin witha dark narrow border. Dimen- 
sions two inches by three and a half. 
eomplanata, shell ovate- quadrangular, hinge-mar- 
gin elevated into a large wing ; valves connate ; ; 
