THE NAUTILUS. 



VOL. XVIII. JULY, 19O4. No 3. 



NOTES ON EASTERN AMERICAN ANCYLI. II. 



BY BRYANT WALKER. 



Ancylns rivularis Say. PI. I, figs. 1-10, 13-15. 



The typical form as established by Haldeman is represented by 

 fig. 3 (the specimen figured agreeing almost exactly with his dimen- 

 sions), and is an ovate, moderately elevated shell with a subacute 

 apex, which is inclined toward the right side, and with about one- 

 third of the shell posterior to it. The anterior and dextral slopes 

 are regularly but not strongly convex ; the posterior slope is quite 

 concave immediately below the apex, but becomes nearly straight 

 toward the peritreme ; the left slope is nearly straight, sometimes 

 slightly concave towards the apex. The lines of growth are well 

 marked but quite irregular, and there is more or less of a tendency 

 to the radial rippling on the anterior slope so common in many 

 species. The shell is distinctly narrowed toward the posterior ex- 

 tremity, the greatest width being just in front of the apex. Asso- 

 ciated with the specimen figured, and grading into it, is a more 

 depressed form, with the apex less prominent'and the posterior slope 

 nearly straight (fig. 4). Similar examples have been supplied from 

 several localities in the neighborhood of Buffalo, N. Y., and indeed 

 it seems to be rather the characteristic form of that region. The few 

 examples seen from eastern Massachusetts are smaller and rather 

 more depressed than the typical form.* Western specimens appar- 



* The "large specimens" from Caribou, Me., quoted by Nylander (NAur., 

 xiii, p. 105) should, I think, be referred to A. parellelus. 



