LYMN^EID^E OF NORTH AMERICA. 125 



these organs indicates that the subgeneric groups, such as Radix, 

 Bulimnea, Galba and Acella, which were founded on shell characters 

 may also be distinguished by differences in the genitalia and radula. 

 Only the North American species have been critically examined. 1 

 The application of the above criteria results in the classification pre- 

 sented below. 2 



Family LYMN^HXE Broderip, 1839. 

 Subfamily LYMN^EIN^E Dall, 1870. 

 Mantle margins retained within margin of shell. 



Subfamily AMPHIPEPLEIN^: Dybowski, 1903. 

 Mantle margins enlarged, covering a portion of the shell. 

 The latter subfamily contains the following genera; neither of 

 which occur in the North American fauna. 



Genus AMPHIPEPLEA Nilsson, 1822. 



Amphipeplea NILSSON, Moll. Suec. Ter. et Fluv., p. 58, 1822. DALL, Ann. 

 Lye. N. H., IX, p. 350. TRYON, S. & S. Conch., Ill, p. 102, 1884. Type, Buccinum 

 glutinosum MULLER. 



"SHELL: Globular, thin and transparent; spire very broad, de- 

 pressed, short ; aperture occupying nearly five-sixths of the entire 

 length of the shell, very broadly expanded; outer lip thin, simple; 

 columella without a fold. 



"Animal with large mantle lobes which partly cover the shell. 

 According to Forbes, Van Beneden found a peculiar modification of 

 the nervous system correlated with the expanded mantle" (Dall). 



Genus CYCLOLIMN^A Dall, 1905. 



Lymn&a, section Cyclolimn&a DALL, Alaska Moll., p. 64, 1905. Type 

 Lymnaa involute, HANLEY. 



"SHELL: Thin, involute, the last whorl as long as the shell, the 

 outer lip thin, simple, not expanded, the inner lip appressed, the axis 

 not plicate, but with a small umbilical chink" (Dall). 



The mantle covers a portion of the shell as in Amphipeplea. 



This subfamily will doubtless show anatomical peculiarities dis- 

 tinctive from those of Lymnaeinse. 



KEY TO GENERA AND SUBGENERA OF RECENT AMERICAN LYMN^AS. 



Prostate bulbous, penis less than half the length of penis-sac; 

 lateral teeth bicuspid; shell with strongly gyrate columella. 



Genus LYMN^A Lamarck. 



1 Several foreign genera are not here included, as their anatomy is un- 

 known. It is not thought that a study of these genera will materially change 

 the classification here presented. 



^This outline was published in Science, n. s., vol. XXVII, No. 702, p. 942, 

 1908. 



