LYMNZIDZ 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.* 
The application of the above criteria results in the classification pre- 
sented below.’ 
Family LymMn21p2 Broderip, 1839. 
Subfamily LymMN.21N# Dall, 1870. 
Mantle margins retained within margin of shell. 
Subfamily AMPHIPEPLEIN2 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 AmMPpHIPEPLEA Nilsson, 1822. 
Amphipeplea Nitsson, Moll. Suec. Ter. et Fluv., p. 58, 1822—Datt, Ann. 
Lyc. N. H., IX, p. 350—Tryvon, S. & S. Conch., III, p. 102, 1884. Type, Buccinum 
glutinosum MULLER. 
“Suet: 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. 
Lymnea, section Cyclolimnea DALL, Alaska Moll, p. 64, 1905. Type 
Lymnea involuta HANLEY. 
“SyeLtL: 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 Lymnzine. 
KEY TO GENERA AND SUBGENERA OF RECENT AMERICAN LYMN EAS. 
Prostate bulbous, penis less than half the length of penis-sac; 
lateral teeth bicuspid; shell with strongly gyrate columella. 
Genus Lymn#a Lamarck. 
1Several 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, 
18s This outline was published in Science, n. s., vol. SEVEN, No; 702) p. 942; 
