234 HELICIO^. 



approaches the aperture, and obtusely angular at the 

 periphery. Beneath forming a broad, crateriform um- 

 bilicus, in which the whorls are displayed to the apex. 

 Aperture oblique, lunate, the lip simple. 



Diameter one-fourth of an inch ; axis one-eighth of an 

 inch. 



Geographical Distribution. Found at Greenwich, 

 N. Y. by Dr. Ingalls, on sticks, leaves, &c. on the very 

 edge of a pond, and in such numbers that he had seen 

 " a thousand under a single plank six feet long." 



Remarks. It may well be doubted whether this is 

 the H. lucida of Europe or not. In the first place, it is 

 difficult to know what shell is meant in the European 

 books, when S. lucida is spoken of. Then, it appears to 

 be larger than the specimens I have seen under that 

 name. Still, small specimens accord so well with Euro- 

 pean examples, that it has been thought best for the pre- 

 sent to regard it as that species. The fact that it has, 

 as yet, been found at only a single locahty, is another 

 reason for supposing it to be an introduced species. It 

 is a third larger, and has a broader and more open 

 umbilicus, than R. arhorea. It is of the size of S. niti- 

 dula; but is a less sohd shell, and less depressed. In 

 some specimens there are opaque patches on the base, 

 caused by a deposition of callus. Dr. Ingalls has distri- 

 buted it under the name of H. hydrojjMla, which name 

 should be adopted, should further observations show it to 

 be a new species. 



