OF CONCnOLOOY. 113 



" How these shells came in the pond is as much a matter of 

 surprise to me as it is to you, I have no knowledge that 

 there was ever a shell put into the pond. 



" One fact more. The spring and pond are perfectly isolated. 

 as the overflow disappears at the edge of a sandy plain in less 

 than ten rods from its fountain-head, and there is no stream of 

 perpetual running water within one mile of it. The Farming- 

 ton River is about a mile distant in the valley below, and here 

 the only species yet found are Lym. columella, Say, Physa he- 

 terostropha, Say, Planorhis hicarinatus, Say, Vivipara decisa^ 

 Say, Unio complanatus, Sol., and U. radiatus, Lam. 



"The pond is two hundred feet above the bed of Farming- 

 ton Biver." 



3. Planorbis (Gyraulus) circumstriatus, Tryon. — t. 10 

 f. 6—8. 



Description. — Shell small, rugose, generally distorted in 

 adult specimens (the whorls not proceeding in the same plane, 

 but elevated or depressed below it at times) ; volutions four, 

 convex, increasing very slowly in diameter, with deeply im- 

 pressed suture, towards the aperture deflected ; below concave, 

 but exhibiting all the volutions, with two or three raised 

 revolving lines; aperture small, very oblique Light horn 

 color. 



Dimensions. — Diameter 6 mill., height IJ mil'i. 



Sahitat. — Artificial pond at Weatogue, Conn. Dr. S 

 Shurtleft". 



My cabinet. Cabinet of Mr. Lea. Cabinet of Dr. Shurtleff. 



Observations. — This species is of the same size as Planorhula 

 armigera, Say, and its upper surface is remarkably like that 

 shell. It differs, however, in its unarmed, oblique aperture, 

 and concave, lineated under surface. 



The deflected aperture reminds one of PI. dejiectus, but from 

 that, as well as parvus and alius, it is distinguished by the 

 slow increase in the size of the whorls. 



The remarkable raised revolving lines are visible on the 

 under surface of all the adults before me, but on a number of 

 young shells I can detect no trace of them. 



Besides the above two species, I find a single specimen of 

 Lym. umbrosa, Say, and several of L. desidiosa, Say, 



