258 



posed corals, rather than a natural ingredient of the 

 water and the source of coralline growth. 



Dr. Jackson exhibited the shells (Alasmodonta arcuata) 

 which were presented at the last meeting by W. E. S. 

 Whitman, Esq., of Gardiner, Me. This species is found 

 in the rivers of Kennebec county, and being lined with 

 a pearly secretion, the shells have been sought for in 

 that neighborhood for pearls. The thanks of the So- 

 ciety were voted for the gift. 



Dr. Weinland called attention to the fact that the outer surface 

 of the shells, near the hinge, was considerably eroded, and he 

 referred to a communication of Dr. James Lewis, of Mohawk, 

 N.' Y., read to the Society February 18, 1857, in which the pres- 

 ence of saline alkalis is assigned as the cause of erosion by that 

 gentleman, contrary to an opinion expressed by himself in a paper 

 read to the Society October 15, 1856. He disagreed with Dr. 

 Lewis upon this point, for he believed that the animal absorbs 

 from the water only such substances as ai'e suited to its nature. 



Dr. A. A. Hayes stated that where the composition of the 

 water is changed at different seasons of the year, there is great 

 liability to erosion. He attributed the effect to the presence of 

 organic acids, as humic and ulmic acids or mixtures of the two, 

 which he said were at certain times sufficiently strong to attack 

 the epidermis of the shell. He referred to changes in the Con- 

 necticut, Concord, and Schuylkill rivers, the last two of which 

 have been so much altered in their composition by impurities 

 introduced in mining operations or otherwise, as to render them 

 more or less destructive to animal life. 



Dr. Weinland remarked that he could not believe any waters 

 to be so strongly acid as to be capable of destroying the epider- 

 mis. In his paper referred to above, which he had read to the 

 Society, he had maintained that the first step of the erosive 

 process vpas the destruction of the epidermis by a worm. 



Dr. Jackson thought from the appearance of the smallest per- 

 forations that the destruction of the shell originally commenced 

 with a worm. 



Mr. T. J. Whittemore observed that the shells in Fresh Pond 



