THE NAUTILUS. 15 



the species belongs, Haldemania can be written as a synonym of that 

 group. Until this is done, the matter must rest in abeyance. 



Leaving the position of the western species, which are outside the 

 scope of this paper, for future consideration, I propose to divide the 

 eastern American species of Ancylus into two sections, characterized 

 as follows : 



1st. Lsevapex, sec. nov. 



Shell usually depressed, apex obtuse or sub-acute, smooth. Type : 

 A. fuscus Ads. 



2. Ferrissia, sec. nov. 



Shell usually elevated, apex acute, radially striate. Type : A. 

 rivularis Say. 



Section Lcevapex. 



This section includes all the larger species of Ancylus, which are 

 characteristic of the lakes and slow-flowing streams of the northern 

 States, the Mississippi Valley and Florida. They are usually found 

 on the reeds, dead leaves and submerged timber in such localities, 

 and are rarely, if at all, found on stones, dead shells, etc., in rapidly 

 flowing streams, where they are replaced by the species of the section 

 Ferrissia. With the exception of A. diaphanus and, possibly, A- 

 obscurus, the spe'cies of this group seem to be wholly lacking in the 

 mountain streams' of the Appalachian region between the Ohio river 

 and Florida. 



I. ANCYLUS FUSCUS Adams (1840). PI. I., figs. 1-9. 



Adams' description calls for a large depressed, elliptical shell, 

 moderately curved at the sides, with a moderately prominent, obtuse 

 apex, slightly behind and to the right of the middle-, 7f mm. long, 

 4^ wide and 1^ high. No mention is made of the outline of the 

 slopes. Haldeman states that all these are rectilinear, while 

 Gould describes the shell as regularly convex. None of these au- 

 thors refer to the surface sculpture. But subsequent writers have 

 assumed that the surface was smooth. 



Specimens answering these requirements are common, and show 

 that the species has an extensive range from Massachusetts west, at 

 least, to the Mississippi Valley and south to New Orleans. I have 

 not seen any specimens from Kentucky, Tennessee, the South At- 

 lantic or the Gulf States east of Louisiana. 



The very limited amount of material examined from Massachu- 



