332 



THE AMERICAN NATURALIST [Vol. XL 



recent origin [italics mine] 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 Co., 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 Sandstone. From the time of the excavation till the 

 summer of 1864 there was water in the artificial pond. It was 

 dry in 1864, but I did not examine for shells, as before the excava- 

 tion I had repeatedly examined the spring, but never found shells 

 of any description. 



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

 accidentally crossing the pond, which was dry, I noticed quanti- 

 ties 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 non descript 

 species. I immediately went to the pond and secured all the 

 Lymnaeans 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 

 running water within one mile of it. The Farmington River is 

 about a mile distant in the valley below, and here the only species 

 yet found are Lymnaea columella Say, Physa heterostropha Say, 

 Planorbis bicarinaius Say, Vivipara decisa Say, Unio complanatus 

 Solander, and Unio radiatus Lamarck. 



