200 Fresh- Water Shelh. 



measured upon the back, constitutes from a little more tlian one 

 half, to about two thirds the whole length of the shell ; surface 

 coarsely wrinkled by the lines of growth, sometimes minutely re- 

 ticulated by revolving lines, and sometimes exhibiting small, 

 plane facets, irregularly disposed. Aperture generally less than, 

 but never exceeding one half the length of the shell ; sub-oval, 

 rather contracted ; right lip thin, with now and then a sub-mar- 

 ginal thickening, within colored reddish-brown ; pillar margin co- 

 piously overlaid with white enamel, not closely appressed at the 

 umbilical region ; fold of the pillar large and oblique ; umbilicus 

 for the most part closed. Length y\ inch, breadth j\ inch, diver- 

 gence 43 to 45c». 



The ayiimal is of a dusky-greenish color, similar to that of the 

 shell, varying like it in intensity, minutely dotted with amber- 

 color. Foot somewhat paler, tongue-shaped, reaching about two 

 thirds the length of the largo whorl wlien in motion, obtusely 

 rounded behind. 



The animal attains maturity and dies about the end of June. 

 At this time the young may be seen with the old, about an eighth 

 of an inch in length, and these continue to grow rapidly during 

 iha season. But after the early part of July it is rare to find an 

 aduH shell containing a living animal. At this time the exterior 

 of the shell is much eroded ; in fact the animals, as they cluster 

 together, actually devour each other's shells ; the aperture becomes 

 white and somewhat chalky, and the brown, sub-marginal callus 

 of the outer lip is thus covered over. 



The most common species found in Massachusetts, and one 

 which it is exceedingly difficult to describe, or to determine, if it 

 has been already described. After much observation, and a com- 

 parison of many individuals collected from various localities, and 

 an exchange of specimens with the most distinguished concho- 

 logists of this country, I have come to the conclusion, that it must 

 be regarded as the L. elodes of Say. Its European analogue is L. 

 pahisiris. The only Massachusetts shell which bears much affinity 

 to it, is L. desicUosa, Avhich is smaller, has a more slender spire, 

 and larger aperture, proportionally. But it is closely related toL. 

 umbrosa and L. rejlexa of the Western and Middle States. The 

 former is more solid, more corpulent, with the whorls and aperture 

 more oblique, and its color darker than that of our shell. The 

 latter has the whorls still more oblique, much less convex, form- 

 ing a much less turretted and regularly tapering spire ; the fold 



