THE NATURAL HIST0RY SURVEY. 259 



Subfamily Limiueinee. 



"Lateral jaws present. Rhachidian tooth simply pointed; 

 laterals provided with numerous denticles. Tentacles flat- 

 tened. Genitalia on right side." (Dall.)f 



GENUS LIMN/EA Lamarck. 



Shell: Spiral, generally thin, corneous, ovately-oblong or 

 elongate; spire long, sharp; aperture oval, generally small; 

 columella with an oblique plait across the middle. 



Animal: With short, wide, rounded foot; head support- 

 ing a vela area; front edge of mantle much thickened, simple, 

 not projecting beyond the plane of the aperture; tentacles 

 much flattened, triangular, the eyes sessile upon the inner 

 bases; other characters as in the subfamily (PL xxxiii, Figs. A, 

 B, C); ova deposited in a jelly-like mass without apparent en- 

 velope. 



Distribution: World- wide, but preferring temperate re- 

 gions. 



KEY TO SPECIES OF LIMN^A.* 



A. Shell 50 to 60 mill, in length. 



a. Aperture and spire about equal in length, the former 



much expanded stagnates 



B. Shell 20 to 40 mill, in length. 



a. Spire attenuated, longer than aperture, the latter 



strongly reflexed; surface very rarely malleated reflexa 



b. Spire and aperture about equal in length; surface nearly 



always heavily malleated; shell wider in proportion to 



length than (a) palustris 



C. Shell 15 mill, or less in length. 



1. Surface distinctly striated, with coarse, raised, spiral 



lines caperata 



2. Surface with fine, impressed spiral lines. 



a. Spire equal to aperture, shell fusiform .catascopium 



c. Spire one-third to one-half the length of the aperture. 

 jSpire sharply conic, aperture two-thirds of length 



columella 



f|Spire depressed conic, aperture three-fourths of 



length woodruffi 



d. Spire two-thirds the length of the shell, which is sca- 

 lariform ferrissi 



3. Surface without spiral lines. 



a. Spire short conic, aperture roundly ovate, not pro- 



duced at the lower part humilis 



b. Spire long and pointed, aperture long-ovate, pro- 



duced at the lower part desidiosa 



tAnn. and Lye. Nat. Hist., Vol. IX, p. 348, et sec. All quotations of Dr. Ball are from 



this work. 



*The account ot the genus Limnaea is a modification of the author's paper in Trans 



Acad. Sci., St. Louis, Vol. IX, No. i, 1901. 



