LYMN^ID^E OF NORTH AMERICA. 233 



CLAY DEPOSITS. 



Canada: Mr. Peel's clay pits near Montreal (Bell); Pleistocene fossil, 

 Montreal (Dawson). 



DRIFT. 



South Dakota: Sioux Falls, Minnehaha Co. (Todd). 



Ecology: "Lymncea caperata I have found almost invariably in 

 ditches and sloughs which are dry during part of the year, with nearly 

 always a fine mud bottom; often in ditches entirely free from vege- 

 tation, with obrussa, and again in sloughs containing much swamp 

 grass, filled by spring overflow of streams." (Henderson, for Colorado 

 specimens.) Among grass in marsh (Humboldt County, Nevada; 

 Richardson). 



In the Mississippi Valley this species seems to almost invariably 

 occupy intermittent streams or small pools, ponds and ditches which 

 dry up in the summer. In Illinois it is usually found in association 

 with Aplexa hypnorum and Sphcerium occidentale, either in small 

 streams, pools or sloughs, or in spring pools in the woods which become 

 completely dry in late spring and summer. The species hibernates 

 to a greater degree than any of the other Lymnseas, a fact attested 

 by the many rest varices observed on the shell of large individuals. 

 In these dry ponds living specimens may frequently be found by dig- 

 ging into the mud under leaves and other debris. The reports of Van 

 Hyning for Iowa, Walker for Michigan, Baker for New York and 

 Sterki for Ohio show the same ecological relations of this species. 



Remarks : Although the statement has been made that caperata 

 may prove a heterogeneous assemblage of different forms, it is never- 

 theless true that it is one of the most distinct and uniform of American 

 Lymnseas. The striking manner in which the epidermis stands erect 

 in the impressed spiral lines is peculiar to this species and will always 

 distinguish it when the specimens are fresh. Some small specimens 

 resemble individuals of cubensis and hnmilis, and have been thus re- 

 ported by various collectors. Caperata is one of the commonest of 

 American Lymnseas and is found over a very wide stretch of country. 

 It varies somewhat in the length of the spire and in the rotundity 

 of the whorls, but this variation is not marked or uniform. (Plate 

 XXVIII.) Specimens from Iowa, Illinois and Indiana are very large 

 and robust. Many specimens are quite scalar and the color variation 

 is wide. The shell is sometimes quite thin, though generally very solid. 

 Individuals from Yukon Territory are smaller and paler than typical 

 caperata, but offer no other tangible characters. They were compared 

 with Say's specimen by Dr. H. A. Pilsbry, who pronounced them iden- 

 tical. Some specimens from California and Wyoming resemble buli- 



