52 



branches from the vertebral artery, coming off with the spinal 

 nerves and going to the skin, and subserving the purspoes of 

 respiration. It is difficult to say, at present, what is the exact 

 analogue of this branch of the pulmonary artery. 



The following connmunication from Mr. James Lewis 

 was read : 



Notes on Paludina decisa Say. By James Lewis. 



Paludina decisa Say, is probably the only species of Paludina 

 to be found in New England and the eastern portion of the State 

 of New York. 



It has been observed, that this species often presents speci- 

 mens that are reversed. From several hundreds of specimens 

 obtained in the Erie Canal, at Mohawk, Herkimer County, 

 N, Y., for purposes of exchange, the embryonic young pre- 

 sented in one lot, a proportion of about one reversed shell to 92 nor- 

 mal ; these were all taken from normal adult specimens. On 

 another occasion, from a similar lot, the proportion was as 1 to 

 55.5 ; giving in the two between 1 and 2 per cent, of reversed 

 specimens (young.) The embryonic young of reversed adults, 

 gave as follows : 



Large reversed adult. 3 reversed young. 13 normal. 



Smaller '' " 2 *' " 12 



Still smaller '' " *' 12 



c( (( (( Q *' ^^ 8 '"'' 



P. decisa obtained near Boston, Mass., first presented to my 

 notice reversed specimens. The same thing has been noticed in 

 other portions of New England. (See " Shells of Vermont, by 

 C. B. Adams, A. M." ) I have also noticed it in Paludina in 

 Mohawk River, a variety of P. decisa, which, owing to the greater 

 abundance of lime in the water, seldom has its spire truncated, 

 o,s is seen in shells found in localities deficient in lime. (I would 

 here remark, that samples of these shells of the normal form, 

 sent to a friend in Boston, were pronounced P. integra Say.) ^ 



In the Erie Canal, these shells, favored by peculiar circum- 

 stances, attain a very large growth, some of them being 1 /g- 

 inches long, by 1 xV wide. They also present, within certain 



