GASTROPODA 509 



Family 2. LYMN^IDAE.* 



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

 flaring aperture, varying from liorn-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. 



LYMNiEA 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 LymncBa here described; 

 Oi Shell more than 25 mm. long. 



&! Spire long and slender L. stagnali8 



62 Spire short. 



Ci Aperture about half the length of the shell L. megasoma 



Cj Aperture almost or quite as long as the shell L. auricularia 



flj Shell less than 20 mm. long. 

 6i Aperture about half the length of the shell or longer. 

 Cx Shell with 4 whorls. 



di Parietal callus straight L. columella 



d^ Parietal callus with a slight fold or angle in the middle. . .L. catascopium 

 Cz Shell with 5 or 6 whorls. 



(Zi Shell 15 mm. long L. obrussa 



^2 Shell 8.5 mm. long .L. humilis 



62 Aperture less than half the length of shell. 



Ci Shell very long and slender, aperture elongate L. reflexa 



C2 Shell not unusually slender. 



di Shell 30 mm. long or less L. palustris 



da Shell 15 mm. long or less with heavy spiral lines L. caperata 



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 -vvhorls, 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 "Lymnaidae of North and Middle America," by F. C. Baker, Chicago 

 Acad. Sci., Special Tub. No. :;, 1911. 



