ANCYLUS. 501 



Slicll dextral, thin, patelliform, depressed, non-spiral. Fig. 751. 

 apex directed to the right ; aperture very wide ; peritreme 

 continuous, simple, entire. 



Jaws three, covered with papilla;, one superior, small, 



Animal 



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

 contiguous to the superior. Enlarged. 



Lingual membrane broad ; teeth crowded, numerous ; central 

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

 the laroer. 



'o^ 



T]ie Ancijli and Acroloxi 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 Ancylus is universally adopted at the present time. 



The shell of Ancylus is dextral, the apex being directed to the 

 right, but 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. 



Ancylus parallelus, Haldeman, Mon. part 2, p. 3 of cover ( 1 846) ; p. 1 1 , pi. 1 , fig. 6 ( 1 844). 

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

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



Ancylus rirul'iris, Gould, Inv. of Mass. 224, fig. 153 (1841), teste Haldeman. — Axon. 

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



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

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

 regularly rounded; apex nearly equidistant from both ex- '° ' 



tremities, nearer to, and leaning to, one side and one end ; ^ ^^mz- 

 aperture oval ; color dark green. Length, one fifth of an Euia"ged 

 inch ; breadth, one tenth of an inch. 



Found on stones and floating leaves in rividets 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 



