ANCYLUS. 501 



Shell dextral, thin, pateUiform, depressed, non-sph-al, Fig. 751. 

 apex directed to the right ; aperture very wide ; peritreme f0^\ 

 continuous, simple, entire. \\M 



Jaws three, covered with papilla, one superior, small, ^-^ 

 transversely oblong, two lateral, long, very slightly arcuate, °^J^^^^' 

 contiguous to the superior. ^''^^'^'•^■ 



Lingual meml)rane broad; teeth crowded, numerous; central 

 minute, narrow, simple ; laterals broad, bicuspid, the inner cusp 

 the larger. 



The Anct/li and Acroh.ri are widely distributed over the globe. 

 In North America the known species are most numerous in those 

 States where conchological observations have most been made, but 

 an equal number may be found in other regions when they come to 

 be explored. They are found in the extreme north and in Mexico, 

 at every station. 



The name Ancijlus is universally adopted at the present time. 



The shell of Aiici/lus is dextral, the apex being directed to the 

 right, V)ut the generative, respiratory, and anal orifices are on the 

 left of the animal, as in Planorbis. 



Ancylus parallelus. 



Fig. 153. 



Shell elongated-oval, sides rectilinear, apex nearer to one side, nearly central. 



Anajliis purallelus, Haldeman, Mon. part 2, p. 3 of cover (1846) ; p. 11, pi. 1, fig. 6 (1844). 

 — Adams, Shells of Vermont, 164 (1842). -De Kay, N. Y. Moll, 13 (1843).— 

 W. G. BiNNEY, Smith. Inst. L. and Fr. W. Shells, ii. 142, fig. 237 (1865). 



Anci/liis rinil'ij-is, Gould, Inv. of Mass. 224, fig. 153 (1841), teste Haldeman. — Anon. 

 Can. Nat. ii. 212, fig. (1857). — Not of Say. 



Shell small, narrow, elongated-oval, the sides nearly parallel, but 

 one end is somewhat narrower tluin the other, and both are 

 regularly rounded ; apex nearly equidistant from both ex- 

 tremities, nearer to, and leaning to, one side and one end ; ^ j,a,,,i. 

 aperture oval ; color dark green. Length, one fifth of an Enlarged. 

 inch; breadth, one tenth of an inch. 



Found on stones and floating leaves in rivulets and ponds. 



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

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



