10 Trans. Acad. Sci. of St. Louis. 



plete membrane, as several examinations gave the result 

 recorded above. 



Distribution: New England to California, Canada to 

 Georgia, Texas and New Mexico. 



Geological Distribution: Pleistocene; Loess. 



Habitat: Similar to that of desidiosa. It seems to prefer 

 the under side of boards, sticks and lily pads. 



Remarks: As remarked under the last species, humilis is 

 closely related to desidiosa. It is always smaller (about one 

 half) is never malleated, and the spire is shorter and more 

 conic and the aperture more rounded. This is one of our 

 most abundant species and may be found by the hundred in 

 any small pond or ditch, attached to submerged sticks, stones 

 or vegetation. It is, like all the Limnaeids, very sociable 

 and is always found in communities. L. desidiosa, caperata 

 and palustris are almost always found associated with this 

 species. It is as frequently out of water as in it, and this 

 fact has led some conchologists to identify it as Pomatiopsis. 

 Not long ago a number of specimens were given to the Acad- 

 emy by a gentleman who said they were found in wet moss 

 but not in the water at all. He thought, from this fact, that 

 they must certainly be a land mollusk. The writer has had 

 this species crawl over his desk like some of the land snails, 

 which fact is true, in a lesser degree, of L. caperata and desid 

 iosa. It is very abundant and universally distributed. 



5. LlMNAEA CAPERATA Say. 



PL I. f. 11. 



Limnaea caperata Say, New Harm. Diss. 2 : 230. 1829. 



Shell: Ovately elongate, rather solid, translucent; color 

 yellowish horn to brown, sometimes black; surface shining or 

 dull; lines of growth numerous and very fine; shell en -ircled 

 by numerous irregular, impressed spiral lines, which give the 

 shell a somewhat latticed appearance; these spiral lines are 

 placed on the epidermis and may be rubbed off with a b: ush ; 

 whorls 5-6, convex, the last less than half the length of the 

 shell; spire long, somewhat acute; sutures very heavily im- 

 pressed; aperture ovate, its termination more or less rounded, 

 frequently reddish or purplish ; peristome thin, sharp ; colum- 



