ANCYLUS. 225 



ing beyond the edge of the aperture ; within 

 bluish-white, darker towards the apex. 



Length 7-5, alt. 3 mill. 



Passaic River, near Patterson, N. Jersey. 



" The specimen which furnished the above 

 description was one of the largest which I 

 have seen. They are more commonly of the 

 dimensions of A. rivularis. I separate it from 

 the latter chiefly on account of its solid, calca- 

 reous structure." I have not seen this species, 

 and can offer no opinion upon it. 



10. ANCYLUS BOREALIS, Morse. 



Plate 2, fig. 7, 8. 



Shell elliptical, solid, light yellow, apex ele- 

 vated, rounded, very obtuse, nearer the poste- 

 rior margin of the shell ; lateral slopes steep, 

 anterior slope slightly convex, near the apex ; 

 posterior slope straight. Fine regularly inter- 

 rupted radiating lines mark the surface of the 

 shell from the apex to the borders ; incremen- 

 tal lines irregular. 



(19) 



