LYMNZIDZ OF NORTH AMERICA. 135 
1874. Limne@a HarTMAN and MIcHENER, Conchologia Cestrica, p. 62. 
1876. Limnea Meek, U. S. Geol. Surv. Terr., final Report, IV, p. 532, 1876. 
1884. Lymnus Tryon, S. & S. Conch., III, p. 101, 1884. 
1902. Limnea BaAxer, Moll. Chi. Area, II, p. 259, 1902. 
1903. Limnus Dyzowsk1, Bull. Acad. Imp. Sci. St. Petersb., XVIII, p. 113, 1903. 
1905. Lymnea Datt, L. & F. W. Moll. Alaska, pp. 59, 63, 1906. 
1908. Lymn@a Baker, Science, n. s. XXVII, No. 703, p. 943. 
SHELL: Ovately-oblong or elongated, generally thin and brittle; 
spire more or less attenuated; last whorl expanded; peristome thin, 
somewhat flaring, without internal varical thickening; aperture ovate 
or oblong-ovate, sometimes rounded; axis gyrate, forming a_ sharp, 
ascending columellar plait; no true umbilicus, but there is occasionally 
a very small chink; columellar callus closely appressed to the body of 
the last whorl, forming a wide deposit; surface marked by numerous 
fine impressed spiral lines and close-set longitudinal growth lines, form- 
ing a finely decussated pattern; a horny periostracum or epidermis is 
poesent. (Pl XVIII, fig. 7.) 
ANIMAL: With a short, wide, rounded foot; head with the usual 
bilobed vela area; surface of body finely striated, presenting a smooth 
appearance ; tentacles, eyes and other characters as in the family. 
JAws: Superior jaw much wider than high; dorsal margin round- 
ed, ventral margin with a central more or less acutely rounded pro- 
jection ; lateral jaws triangular, the lower angle produced into a long 
tongue-like projection. (Pl. VI, fig. A.) 
Raputa: With unicuspid central tooth and bicuspid lateral teeth; 
marginal teeth serrated. (Pl. VII, fig. A.) 
GENITAL SysTEM: Penis-sac very large, penis very short (about 
one-quarter the length of penis-sac) ; penis-sac retractors normally two 
in number, very large; protractors of penis-sac very large, massive; 
prostate forming a bulb-like enlargement at the entrance of the prostate 
duct; the distal portion of the prostate is constricted behind the en- 
larged portion and is somewhat fusiform in shape; receptaculum 
seminis rounded, its duct of rather smail diameter; lower portion of 
oviduct very long; first accessory albuminiparous gland rounded. (PI. 
png. A.) 
Type: Helix stagnalis Linné. 
DistriBuTION: Holarctic region of America, Europe and Asia. 
The genus Lymnea is here restricted to include those species 
having a bulb-shaped anterior termination of the prostate, differing 
in this character from all known groups of Lymneide. The penis-sac 
retractors are normally two in number and are very massive. The 
