123 



Since identifying these forms as nnere local varieties of one 

 species,'my attention has been drawn to another local modifica- 

 tion of the shells I am induced to regard as a variety of L. catas- 

 copium^ to explain which, requires an allusion to the localities in 

 which the shells are found. 



These shells, having the form of L. caf.ascopiu7n, abound in the 

 Erie Canal, at Mohawk, Herkimer Co. N. Y. From the canal, 

 many other contiguous waters, (pools, ditches, and creeks,) derive 

 many of the shells that abound in them ; and more especially is 

 this shown at certain places where the waste waters from the 

 canal find their way into small shallow streams, either through 

 waste gates, or over the sides of aqueducts, that have their sides 

 no higher than the greatest fulness of the canal requires. 



Into a small stream, known as Fulmer's Creek, (Mohawk, 

 N. Y.) considerable waste water from the canal is discharged, 

 bearing along small chips and bits of flood wood, having upon 

 them the germs, or young of Pliysa^ Lymnea, &c., and these find 

 a resting-place at various spots along the shallow portions of the 

 stream, and, under the modification of a very difl^ereni locality, 

 assume a very different form of growth from what may be ob- 

 served in the locality where they originated. (It may be well to 

 remark, that in that part of the creek above the canal, there are no 

 shells of any kind, while below, they are somewhat numerous.) 



In comparing the two forms of shells found in the canal and 

 creek, the following characters will be found most conspicuous. 



In the canal, the shells have but a {g\\ whorls, and those rapidly 

 enlarged ; the aperture about as long as the spire ; the shells 

 somewhat ponderous, but less so than may be observed in L. ca- 

 iascopium in more favorable localities. In the creek, the shells 

 assume the elongated spire and increased number of whorls 

 observable in L. elodes ; the aperture, instead of being about 

 equal to the length of the spire, is frequently about one third the 

 length of the whole shell, sometimes a little less ; and generally, 

 those shells found in .the creek, are such as would at once be 

 considered L. elodes^ though there are a great number of forms 

 to be found intermediate to the two forms most remote. The 

 eflTect of locality, in addition to the modification of form, is also 

 to change the color of the shell ; those in the canal, when cleaned 



