GASTROPODA 509 



FAMILY 2. LYMN^EIDAE.* 



Shell thin, usually with a prominent acute spire and a large, often 

 flaring aperture, varying from horn-colored to black; lip acute and 

 simple; parietal wall of aperture with a white callus which entirely or 

 partially covers the umbilicus; tentacles flattened; eggs laid in a jelly; 

 radula with unicuspid central tooth: several genera with several hun- 

 dred species, inhabiting ponds, swamps, and streams in all parts of the 

 globe, but principally in temperate regions; about 35 species in the 

 United States. 



LYMNJEA Lamarck. Jaw composed of 3 pieces, 1 large transversely 

 elongate piece and 2 small ones; foot rounded behind: over 200 species, 

 65 American. 



Key to the species of Lymncea here described: 

 ! Shell more than 25 mm. long. 



&! Spire long and slender L. STAGNALIS 



& 2 Spire short. 



(?! Aperture about half the length of the shell L. MEGASOMA 



c 2 Aperture almost or quite as long as the shell L. AUBICULABIA 



a, Shell less than 20 mm. long. 



&! Aperture about half the length of the shell or longer. 

 G! Shell with 4 whorls. 



d v Parietal callus straight L. COLUMELLA 



d 2 Parietal callus with a slight fold or angle in the middle. . .L. CATASCOPIUM 

 c 2 Shell with 5 or 6 whorls. 



di Shell 15 mm. long L. OBBUSSA 



d a Shell 8.5 mm. long L. HUMILIS 



6 2 Aperture less than half the length of shell. 



c x Shell very long and slender, aperture elongate L. BEFLEXA 



c 3 Shell not unusually slender. 



</! Shell 30 mm. long or less L. PALUSTBIS 



d a Shell 15 mm. long or less with heavy spiral lines L. CAPEBATA 



L. stagnalis (L.) (Fig. 776). Spire of shell long and slender, with 

 an acute apex ; aperture flaring ; whorls 6 ; length 60 mm. ; width 25 mm. : 

 circumpolar, being found in the northern states from the Atlantic to the 

 Pacific; often common in ponds; the largest species; Europe. 



L. columella Say. Shell extremely thin and fragile, greenish or 

 yellowish in color, with 4 whorls, of which the last is large and forms 

 nearly the whole shell; length 17 mm.; width 6 mm.; aperture ovate: 

 central and eastern states; often common in stagnant and miry pools 

 and streams. 



L. megasoma Say. Shell thick, with a short spire; length 40 mm.; 

 thickness 25 mm.: northern states from Vermont to Michigan. 



L. reflexa Say (Fig. 777). Shell long and slender, fragile, with 6 

 to 7 whorls; aperture rather narrow; length 40 mm.; width 13 mm.: 



* See "Lymnseidae of North and Middle America," by F. C. Baker, Chicago 

 Acad. Sci., Special Pub. No. 3, 1911. 



