LYMN^EID^E OF NORTH AMERICA. 331 



suggestive. Mr. Tryon writes as follows i 1 "The circumstances uncler 

 which this and the following species were found are so peculiar that 

 it is with great hesitation that I have ventured on a description of either 

 of them. That new species of these shells should exist undetected in 

 sections of the United States which have been so well explored by 

 assiduous naturalists would be surprising; but in the present instance 

 the almost irresistible supposition is that these species are of very recent 

 origin (italics the writer's) — in fact, contemporaneous with that of 

 the body of water which they inhabit. I have looked in vain for some 

 evidence upon the specimens themselves of the effect of some strong 

 local influence. The species are so distinct that they afford no clew 

 to a possible derivation from others. 



"In conclusion, I present the following interesting particulars : 



"Extract from a letter from the late Dr. S. Shurtleff to Isaac Lea, 

 Esq., Weatogue, Hartford County, Connecticut, November 22, 1865. 



"In the summer of 1860 I made an excavation some two rods 

 below a spring that flows about eight months in the year. The spring 

 comes from a neighboring hill. The overlying rock is New Red Sand- 

 stone. From the time of the excavation till the summer of 1861 there 

 was water in the artificial pond. It was dry in 1864, but I did not 

 examine for shells, as before the excavation I had repeatedly examined 

 the spring, but never found shells of any description. 



"After my return from Pennsylvania, in September, 1865, acci- 

 dentally crossing the pond, which was dry, I noticed quantities of 

 shells clustered in the hollows. I gathered a few and laid them by 

 for leisure examination; when I came to look at them again I found 

 L. umbrosa, as I supposed, as well as a nondescript species. I imme- 

 diately went to the pond and secured all the Lymnseans I could find — 

 some alive and many dead ; and, fearing the dry season would destroy 

 them all, I put many of the living shells into a pond that I have since 

 made, that will never dry up. I may have collected 50 specimens of 

 L. umbrosa (?) and of other specimens a half-pint. 



"How these shells came into 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 run- 

 ning water within one mile of it. The Farmington River is about a 



'Amer. Journ. Conch.. TI, p. 112, 1866. 



