316 THE CHICAGO ACADEMY OF SCIIiXCIiS. 



precarious environment. The specimens from Thunder Bay Island ex- 

 hibit admirably the effect of the heavy seas of Lake Huron. 



Remarks : Alpcncnsis may be distinguished by its solid, narrow 

 shell, long, acute spire, rounded whorls, with well rounded body whorl 

 and particularly by its inner lip, which is wide and raised from the 

 columellar region, producing an emarginate condition very similar 

 to that in Galba emarginata. The solidity of the shell and particularly 

 of the inner lip, which is nearly always continuous will also serve to 

 aid in the identification of this race. Some small specimens somewhat 

 resemble Galba palustris desidiosa, but that race is smaller, thinner, 

 the spire is regularly turreted, the body whorl is proportionally wider 

 and more obese and the inner lip is appressed to the parietal wall, pro- 

 ducing a distinct plait. Galba elodes has a narrower shell with more 

 flat-sided whorls and a more elongate aperture. 



This form is so numerous in individuals and so constant in char- 

 acter that it seems necessary to bestow a name upon it as a race of 

 palustris. Typical palustris from this locality lives in a still, swampy 

 area which is protected from the rough waters of Lake Huron by a low 

 shore. This quiet, peaceful habitat produces a large, thin shelled form 

 quite unlike the race which lives on the exposed shore (see plate XXVI, 

 figures 17-20; compare with figures on plate XXXIII). The environ- 

 ment in this case has produced a shell which is uniformly so distinct as 

 to be as easily distinguished as are any of the species of Lymncea. At 

 Halma, Minnesota, a narrow shell occurs, but this is connected by 

 insensible degrees with the large corpulent form of typical palustris 

 (see plate XXVI, figures 21-26). In Owasco Lake, N. Y., a narrow, 

 long spired form occurs, but here again the variation runs into the 

 typical form without a break. In alpcncnsis, the peculiarities are quite 

 uniform and there is no decided variation towards the large, corpu- 

 lent form. Young shells have a short spire and elongate-ovate shape, 

 but the fully adult shell is always as figured on the plate. The shells 

 were collected by Dr. William A. Nason of Algonquin, Illinois. 



Galba palustris desidiosa 1 (Say). Plate XXXIV, figures 1-12. 



Lymneus desidiosus Say, Journ. Phil. Acad., II, p. 169, 1821; Long's Exped., 

 II, p. 264, 1824; Binney's Ed., pp. 66, 130, 1858. 



Limneus desidiosus Say, Amer. Conch., VI. p. 211, pi. 55, fig. 3, 1834; 

 Binney's Ed., p. 211, 1858. 



Limncea desidiosa Binney, L. & F. W. Sh. N. A., II, p. 48, 1865. — Gould, 

 Inv. Mass., p. 219, 1841 (part) ; Binney's Ed., p. 470, 1870 (part). 



1 0nly those references are here given which are believed to refer to the 

 true desidiosa. Several references listed under obrussa may belong- here, but 

 there appears to be no way of verifying them. 



