212 Fresh-Water Shelh. 



respect similar to P. hi/jJnOrum of Europe, unless perhaps, its 

 spire may be somewhat more produced. 



It is not very common in Massachusetts, and is seldom found 

 as lono" as the above dimensions; while Mr. Say gives it y\ of an 

 inch in Illinois. 



It probably belongs to the genus iVi-LExus of Gvny {Turton^s 

 Man., 255), which he institutes upon the elongated form of the 

 shell, the want of auricles at the base of the mantle. This latter 

 point I did not notice, when the animal was before me. 



Mr. Say describes the animal as black, and spotless above and 

 below ; tentacuia with a white ring at base. He must have 

 observed them at a more advanced age than any I have seen 

 living ; or else the species observed are diflerent. 



Genus ANCYLUS, Muller. 



Shell hoat-shaped, without a spire, apex jjointed, inclininr/ for- 

 wards and to one side ; aperture ovate. 



It is not yet satisfiictorily determined under what family this 

 genus should be arranged. Its animal is closel}^ allied to the 

 LiMNEANA, and its natural relations are certainly stronger to this 

 family, notwithstanding the form of the shell, than to the 

 Calypt.sa'cea, where it has usually been placed. 



A'ncylus Rivularis. — (Say.) 



Shell small, narrow, elongated-oval, the sides 

 (f^^ nearly parallel, but one end is somewhat narrower 



^' than the other, and both are regularly rounded ; 



apex nearly equi-distant from both extremities, nearer to, and 

 leaning to, one side and one end ; aperture oval ; color dark-green. 

 Length i inch, breadth j\ inch. 



Found on stones and floating leaves in rivulets and ponds. 

 It is closely allied to A. fluviadilis of Europe ; but the apex is 

 less acute and more central. There is another American species, 

 the A. tardus, Say, wnich has been found by Professor Adams in 

 Vermont, but which I have not yet found in this State. It is much 

 more rounded and conical than this, and the apex is not lateral. 



A'ncylus Fuscus. — (Adams.) 



Shell small, very thin and pellucid, of around oval 



^^»form, the entire outline regularly curved; depressed 



and regularly convex, not compressed at the sides • 



