ANCYLUS FUSCUS. 13 



little narrowed posteriorly; lateral margins 

 slightly convex: anterior, posterior, and lateral 

 slopes, rectilinear: apex very obtuse, subcentral: 

 epidermis extending beyond the peritreme. 



Color translucent pale yellow, epidermis 

 fuscous, frequently discolored so as to appear 

 dark brown. 



Dimensions. Long. 7.5, lat. 5, elev. 2 mill. 



Geographical Distribution. Inhabits Fresh 

 Pond, near Harvard, Massachusetts. 



OBSERVATIONS. 



This large species is remarkable for the 

 manner in which the periostraca extends beyond 

 the margin of the shell, upon the object to 

 which the mollusk is attached; so as to give to 

 the limb the aspect of being reflexed. 



