198 



Fresh- Water Shells. 



pool in Cambridge, I thouglit Avas siifiiciently distinct to be regard- 

 ed, as a new species ; and I accordingly gave its characters under 

 tbe name oi Lim.nce'a dialy'hea^ in Sillimau's journal, xxxiii. 196- 

 But as it has not been found in any other place, I am now dispos- 

 ed to regard it as a strongly marked local variety of L. columella. 

 It is very possibly such a shell to Avhich Wx, Say alludes in the 

 " Journal of the Academy of Xatural Sciences," ii. 1G7, as " L. 

 columella^ var. a. small, black, from Cold AVater Creek, 'Missouri." 



LiMN.^:^^. Maorostoma. — (Say;) 



Shell fragile, pellucid, light horn-colored, ov- 

 ate-conical ; last whorl very large, moderately 

 inflated, surmounted by three very small, obhque 

 ones, forming an acute apex ; surface shining, 

 marked by line lines of growth, which are cross- 

 ed and rendered tlexuous by numerous revolving 

 hues, faintly visible without a magnifier ; suture distinct, the 

 whorls approaching it by a gradual slope ; aperture ovate, very 

 ample, four-fifths the length of the shell, and, when mature, broad- 

 ly expanded ; outer lip very sharp and thin, broadly rounded in 

 front, and, maintaining its sharp edge, it rises and disappears 

 within the sliell ; pillar so broadly arched as to allow a vicAv of 

 much of the interior of the spire ; a minute umbilicus is formed 

 by a retiected scale of enamel ; in mature shells a glazing of ena- 

 mel is found upon the preceding whorl as it encroaches upon 

 the aperture. Length ii inch, breadth ■^•-^ inch, divergence ITS''- 

 This shell is closely allied to L. columella, and in an immature 

 state is not easily distinguished from it ; but that shell is much 

 more elongated, and regularly tapering, the divergence of the 

 spire being not more than GO^. Such specimens Professor Adams 

 described as his L. acuminata. But at maturity the shell is very 

 distinctly ciiaracterized by its widely spreading outer lip, Avhich 

 gives great expansion to the aperture. Mr. Say receiA^ed it from 

 the rice-fields of Carolina. It is the analogue of the L. ovdtus, of 

 Europe. 



Limx^'e'a Desidiosa. — (Say.) 



Shell ovate, thin and fragile, the spire elongat- 

 ed and turreted ; color a pale, dirty yelloAvish- 

 green ; Avhorls five, very convex, and for tbe most 

 part suddenly contracted above, so as to present a 

 ■onspicuous shoulder; tbe tAvo or thi-ee uppermost Avhorls are 



