Fresh- Water Shells. 197 



Limn.e'a Columella. — (Say.) 



Shell ovate, ventricosc, extremely tliiu 

 and fragile, transparent, of a pale-greenish 

 or yellowish color, the apex acutely pointed; 

 whorls four, of whieh the last is much 

 inflated, and composes nearly the whole 

 shell ; the upper ones are very small, form- 

 ing an acute apex ; surface with conspicuous and nearly regular 

 lines of growth, minutely waved by revolving lines, some of which 

 are distinctly elevated ; suture slightly impressed ; aperture large, 

 four fifths the length of the shell, generally somewhat dilated ; lip 

 very sharp, ending with a small curve behind ; on the left margin 

 the edge is slightly turned over a minute umbilicus, and forms a 

 considerable fold ; a thin, closely adhering enamel stretches 

 across from it to the angle of the aperture ; the inner lip is so 

 arched as to display a considerable portion of the interior of the 

 shell. Length -^-^ inch, breadth y^o inch, divergence 68° ; of an- 

 other specimen, length if inch, breadth f*^ inch, divergeiice 56*"'. 

 Inhabits stagnant pools and miry places, and is common. It is 

 found at maturity very early in the spring. 



The animal is large, semi-transparent, of a dusky or light-drab 

 color, dotted with silvery white. It is very sluggish in its mo- 

 tions. The head above is slightly tinted with lilac. 



This very brittle shell has rather the aspect of Succi'jstea, than 

 of LiMNJS^A. It varies a good deal in form, being in some speci-^ 

 mens rather slender, and in others broad and distended. The 

 aperture is usually somewhat dilated, especially at its broadly-round- 

 ed base ; but occasionally the outer lip is pressed inwards. 

 The surface is shining, and delicately corrugated by revolving lines. 



Var. Chaly'bea. Fig. 145. 



The spire is more pointed, its di\'ergenee being 



only oQo ; the aperture is more expanded, and the 



fold on the inner hp more obvious. It is thin, but 



not very brittle, ringing like hard-burnt crockery. 



The last whorl is particularly detached from the 



preceding one, so as to form a thread-like channel 



at the suture. The enamel rests loosely against the shell, and is 



wrinkled. The exterior is covered by a bluish-black pigment, not 



easily removed, and the interior has a steel-blue or black-lead color. 



This shell, which I found two years in succession in a muddy 



