MYA, 



eellate, 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 ; ligument concealed ; epidermis sea- 

 green, obscurely radiated ; bluish-white within 

 and tinged with violet. Dimensions two inches 

 and a half by four. 



parva, shell oblong-ovate, small, convex, sides 

 rounded; beaks slightly elevated ; 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. 



arcuata, shell ovate, elongated transversely, thick : 

 base arched, ligament elevated, beaks depressed, 

 cicatrices rough ; epidermis brownish-black ; 

 surface smooth in the young state, eroded and 

 scabrous when old ; teeth two in the right and 

 one in the left valve ; bluish-white within. Di- 

 mensions two inches by four. 



rugosa, 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 with a dark narrow border. Dimen* 

 eions two inches by three and a half. 



complanata, shell ovate-quadrangular, hinge-mar- 

 gia elevated into a large wing ; valves connate : 



