OF NORTH AMERICA. 179 



form, the posterior portion long, narrow and ribbon-like. Female or- 

 gans not differing materially from those of Lymncua (pi. X, fig. C). 



DISTRIBUTION : Holarctic region of Europe ; introduced into 

 America. 2 



This genus differs from all other known groups of Lymnseidae 

 in the very long and narrow penis which can scarcely be differentiated 

 from the vas deferens. There is a different disposition of the retrac- 

 tor muscles, especially in the form of the penis-sac insertions, and the 

 prostate is more regularly pyriform and totally unlike any of the 

 other groups. The vas deferens is also very long. The shell is pecu- 

 liar in its strongly twisted columella and in its ample and expanded 

 body whorl and its perforated (often wide) umbilical chink. Until the 

 anatomy of more of the Lymnaeas is known, the position of some species 

 must remain doubtful. Lymncca randolphi Baker has been placed by 

 Dr. Dall in Radi.v and the shell certainly has many characteristics in 

 common with auricularia, but its position will remain doubtful until 

 the animal is examined. Its position at the present time is thought to 

 be with Stagnicola. 



^adix auricularia (Linne). Plate XXII, figures 12-15. 



Helix auricularia LINNE, Syst. Nat., Ed. X, p. 774, 1758. BAKER, Science, 

 n. s., XXVIII, p. 943, 1908. 



Limncea auricularia MOQ.-TAND., Hist. Moll. Fr., II, p. 462, pi. 33, fig. 21-31, 

 1855. CPR. Rep. Brit. Ass., 1856, p. 222, BINNEY, L. & F. W. Sh. N. A., II, 

 p. 31, fig. 35, 1865. BAKER, Nautilus, XV, p. 59, 1901. Nautilus, XVI, p. 58, 

 1902; Moll. Chi. Area, II, p. 408, fig. 138, 1902. CALL., Science, XVI, p. 65, 

 1902. LETSON, Bull. N. Y. State Mus., LXXXVIII, p. 52, 1905. WHEAT, Bull. 

 Brook. Conch. Club, I, p. 10, 1907. 



Lymncea auricularia BAKER, Amer. Nat., XXIX, p. 675, fig. 10, 1905; Bull. 

 111. State Lab. N. H., VII, p. 102, 1906. 



SHELL : Roundly ovate, inflated, thin ; periostracum horn-color 

 to pale gold ; surface shining, lines of growth fine, wavy, crowded, with 

 occasionally a heavy ridge representing a rest period ; spiral, impressed 

 lines present but very fine ; whorls four, convex, inflated, the last large 

 and spreading; spire short, conic, very small compared with the body 

 whorl ; sutures deeply impressed, channeled in some specimens ; aper- 

 ture very large, ovate, occupying four-fifths of the length of the entire 

 shell, rounded above and flaring below in old specimens ; peristome 

 thin, sharp ; columella sigmoid, the axis strongly twisted forming an 

 erect, sharp ascending plait; callus very thin, closely appressed to the 



2 Until the anatomy of all the American species is known, the distribution 

 of Radix must remain uncertain. At present, no American species is known 

 which can be placed in this group. 



Although this species is not native to America, it has been thought best 

 to include a full description as it is the type of the genus and has also been 

 introduced into a number of our greenhouses. No attempt has been made to 

 include the European synonymy. 



