LYMX^EID^: OF NORTH AMERICA. J35 



1874. Limncea Hartman and Michener, Conchologia Cestrica, p. 62. 



1876. Limncea Meek, U. S. Geol. Surv. Terr., final Report, IV, p. 532, 1876. 



1884. Lymnus Tryox, S. & S. Conch., Ill, p. 101, 1884. 



1902. Limncea Baker, Moll. Chi. Area, II, p. 259, 1902. 



1903. Limnus Dyeowski, Bull. Acad. Imp. Sci. St. Petersb., XVIII, p. 113, 1903. 

 1905. Lymncca Daix, L. & F. W. Moll. Alaska, pp. 59, 63, 1906. 



1908. Lymncra Baker, Science, n. s., XXVII, Xo. 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 

 present. (PI. 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. (PI. VI, fig. A.) 



Radula : With unicuspid central tooth and bicuspid lateral teeth ; 

 marginal teeth serrated. (PI. 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 small diameter; lower portion of 

 oviduct very long; first accessory albuminiparous gland rounded. (PI. 

 X, fig. A.)' 



Type : Helix stagnalis Linne. 



Distribution : Holarctic region of America, Europe and Asia. 



The genus Lymncea 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 Lymnasidge. The penis-sac 

 retractors are normally two in number and are very massive. The 



