216 INVERTEBRATA OF MASSACHUSETTS. 



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 T 5 7 inch, divergence 68 ; of an- 

 other specimen, length j inch, breadth T 4 T inch, divergence 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'NEA, than of 

 LIMNJE'A. It varies a good deal in form, being in some specimens 

 rather slender, and in others broad and distended. The aperture is 

 usually somewhat dilated, especially at its broadly-rounded base ; but 

 occasionally the outer lip is pressed inwards. The surface is shining, 

 and delicately corrugated by revolving lines. 



Var. CHALY'BEA. Fig. 145. State Coll., No. 72. 



The spire is more pointed, its divergence being only 50 ; the 

 aperture is more expanded, and the fold on the inner lip more 

 obvious. It is thin, but not very brittle, ringing like hard-burnt 

 crockery. The last whorl is partially detached from the preced- 

 ing one, so as to form a thread-like channel at the suture. The 

 enamel rests loosely against the shell, and is wrinkled. The ex- 

 terior 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 pool 

 in Cambridge, I thought was sufficiently distinct to be regarded as a 

 new species ; and I accordingly gave its characters under the name of 

 Limn&a chaly'bea, in Silliman's Journal, xxxiii. 196. But as it has 

 not been found in any other place, I am now disposed to regard it as 

 a strongly marked local variety of L. columella. It is very possibly 

 such a shell to which Mr. Say alludes in the " Journal of the Acad- 

 emy of Natural Sciences," ii. 167, as " L. columella^ var. a. small, 

 black, from Cold Water Creek, Missouri." 



