28 



Canal, clinging to the stones of the embankment, at the margin 

 of the water. At the close of navigation, each winter, the level 

 of the water is reduced, so that usually there is scarcely more 

 than a thin stratum at the bottom of the canal. 



In the spring, before the opening of navigation, many of these 

 Lymnsese may be found in the spaces' between the stones of the 

 embankment, far above the water, and in positions where it may 

 be safely assumed they have passed the winter. A greater por- 

 tion of the shells so found, will be observed to have the orifice of 

 the shell closed with a thin transparent membrane, behind which 

 the animal reposes, alive, awaiting the coming of the condition 

 favorable for renewed activity. This fact may be one of import- 

 ance to those persons who are interested in tracing the connection 

 between Lymnczm and Helices, in which latter it is not at all un- 

 common to observe this peculiar membrane, or epiphragm. 



Previous to the enlargement of the Erie Canal at Mohawk, 

 the canal at the " upper lock " was about sixty or eighty feet 

 north of its present position, and the former bed of the canal for 

 a short distance, and the " old lock " now remain, as several 

 puddles or pools of water, in which may be found many shells 

 no doubt descendants of the ancestors of those which may be 

 also found in the canal proper, at this time. It is worthy of 

 remark, however, that those shells which are found in the most 

 shaded places, amid the ruins of the " old lock" are most like 

 the shells found in the canal ; and those shells which are found 

 more remote from the shade of the lock, and in warmer loca- 

 tions, are of a laj^er and coarser growth, and to one not 

 acquainted with these facts, might appear to be different species. 

 Those shells found most remote from the lock, are subject to 

 various changes of conditions; the water frequently dries away? 

 even so much that the mud becomes hard and fissured ; the shells 

 disappear, but reappear again in the spring, and reach a growth 

 that is never seen in the shells found in the more equally tem- 

 pered water of the canal. 



The apparent differences between the shells found in the canal, 

 and those found in those parts of the old canal bed most liable 

 to changes, are as follows : — 



The latter grow to nearly twice the length of the former. 

 The canal shell is of a uniform color generally ; the " old lock " 



