220 INVERTEBRATA OF MASSACHUSETTS. 



Shell ovate, thin and fragile, the spire elongated and turreted ; 

 color a pale, dirty yellowish-green ; whorls five, very convex, and 

 for the most part suddenly contracted above, so as to present a 

 conspicuous shoulder ; the two or three uppermost whorls are 

 very small, and the body whorl about seven tenths the length of 

 the whole shell ; surface generally dead, and somewhat checked 

 with irregular revolving and longitudinal raised lines ; aperture 

 large, usually three fifths the length of the shell, oval, broadly and 

 sub-equally rounded both behind and before ; the lip is consider- 

 ably everted in front, and along the left margin, where it is not 

 closely appressed to the whorl, and leaves a small, but evident 

 umbilical opening ; callus rather abundant ; fold on the pillar 

 slight, and smoothly rounded. Length \ inch, of aperture f inch, 

 breadth fa inch, divergence 45. 



This species is found in most regions, about the muddy margins 

 of ponds and pools. 



It is intermediate between L. elbdes and L. modicellus. Its spire is 

 proportionally more slender, its suture deeper, its aperture proportion- 

 ally larger and more oval, the fold of its columella much less conspic- 

 uous, and it is a much more fragile shell than the former. The latter, 

 while it has the large, oval aperture, the deep suture and shouldered 

 whorls, is still more fragile, of a deep green-color, and is a short, in- 

 flated shell, with a much greater divergence of the spire, and with one 

 whorl more than L. desidiosa. The habits of the two last are similar, 

 but the animal of desidiosa is a much lighter green, and has not the 

 remarkable white dots between the tentacula. 



The characters of the aperture and spire seem to be constant ; that 

 is, the aperture is always large and broadly rounded behind ; and the 

 spire is tapering, the two whorls at the tip seeming somewhat as if 

 superadded ; so that if a line should pass down one side so as to touch 

 all the whorls, this line would be concave. The only variations I have 

 noticed are, that the suture is sometimes shallow, and the shoulder 

 nearly wanting, so as to render the spire more regularly tapering. 

 Mr. Say's description is not definite, and his figure is much shorter 

 than the dimensions he ascribes to it. He gives its length seven tenths 

 of an inch, while it rarely exceeds half an inch. 



