1869.] 151 [Perkins. 



pit on either side of it, and a small rudimentary lateral tooth on each 

 side of the shell; left valve with two scarcely diverging cardinal teeth 

 separated by a deep pit; hinge margin thin, not very broad; pallial 

 impression deep, simple; muscular impression rather deep; epidermis 

 chestnut brown, interior pearly white. Length twenty three mill. 

 (.9 in.), breadth twenty one mill. (.82 in.), height twelve mill. 

 (.48 in.). 



Animal with mantle open, light yellow, edged with a cord of bright 

 orange, edge plain; gills not large, two on each side, very unequal, 

 inner much largest, somewhat rhomboidal ; outer subtriangular united 

 to the inner behind and so appearing like a reflexed portion of it; 

 white, finely striated ; foot thin, tongue-shaped, when fully extended 

 nearly as long as the shell, when contracted wedge-shaped; color 

 bright orange striped longitudinally with light yellow ; palpi not long, 

 broadly lanceolate; siphons none, merely an opening in the mantle 

 serving instead ; ovaries full of bright orange ova in April . 



MEASUREMENTS. 





Length of foot 9 mill, (contracted). 



Breadth 4 mill. 



" outer gills 6.6 " 



" 8.8 " 



" inner " 9 " 



U Q u 



" palpi " 4 « 



" 2.2 " a 



This shell in some respects approaches the 

 semisulcata Leach, and still more closely castanea 

 Say, but aiFords good differences. From the 

 former it differs in form, being broader and not 

 as long, in its greater thickness, smaller and 

 more numerous ridges continued to the edge, 

 broader lunule, and more prominent and curved 

 beaks. It differs from the latter in its much 

 narrower hinge margin, smaller .and less prom- 

 inent teeth, less elevated beaks, less oblique and narrower outline, 

 and strong ridges. To show its differences in form I give com- 

 parative measurements. 



* 

 A. castanea Say. A. semisulcata Leach. A. lutea nobis. 



Length 23 mill. .9 in. 23 mill. .9 in. 23 mill. .9 in. 



Breadth 24.4 " .95 in. 19.4 " .77 in. 21 " .82 in. 



Height 13.4 " .53 in. 8.4 " .34 in. 12 " .48 in. 



