222 INVERTEBRATA OF MASSACHUSETTS. 



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 al- 

 ready described. After much observation, and a comparison of many 

 individuals collected from various localities, and an exchange of speci- 

 mens with the most distinguished conchologists 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. palustris. The only Massachusetts 

 shell which bears much affinity to it, is L. desidiosa, which is smaller, 

 has a more slender spire, and larger aperture, proportionally. But it is 

 closely related to L. umbrosa and L. reflexa 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, forming a 

 much less turretted and regularly tapering spire ; the fold of the pillar 

 much less prominent, and the color yellowish. After all, these species 

 are so nearly allied, that no description, and perhaps no figure will en- 

 able a person to determine any one of them by itself. They must be 

 learned by comparison, and by interchanging specimens. But the diffi- 

 culty does not end here. It is no easy matter to assign the limits of the 

 species. No one presents a greater variety. The length of mature 

 shells varies from half an inch to an inch ; and it is remarkable that 

 the largest specimens are usually the most fragile. The surface 

 usually has an uneven, unfinished, inelegant aspect, coated with mud ; 

 but occasionally we find the conformation of the shell perfectly regu- 

 lar, the color a shining greenish horn-color, and the surface smooth 

 and beautifully reticulated with longitudinal and revolving lines. It is 

 then a very pretty, fragile shell. The aperture is small in proportion 

 to the shell, generally rather contracted ; again, we find the lip begin- 

 ning to expand, and in some specimens received from Vermont, which 

 I suppose to belong to this species, the lip is broadly flaring. Young 

 specimens might be confounded with L. umbilicata, L. desidiosa, L. 

 modicellus, and L. caperdta ; but a little attention to the umbilicus, 

 the aperture, the color, and the revolving lines will enable us to dis- 

 tinguish them, respectively. The umbilicus is usually entirely ob- 

 structed by the overlaying callus ; but in some specimens it is par- 

 tially open. 



