AND ALLIED FORMS. 



Having receutly found some of these animals living in the 

 District of Culumbia, and received from my friends Messrs. 

 Biuney, Tryon, and others, numerous specimens preserved in 

 spirits from other parts of the country, I have been able con- 

 veniently to study their structure and habits, with the view of 

 determining their relations to each other and to neighboring 

 groups. Before giving the results of this study, it will be proper 

 to review what has been already published upon the subject in 

 this country.* 



Mr. S. S. Haldeman and Dr. A. A. Gould were the first in this 

 country to call attention to the generic distinctness of certain small 

 shells previously referred to Paludina, to include which they pro- 

 posed to establish a new genus, Amnicola. This genus was first 

 published by the former gentleman in October, 1840, in a " Supple- 

 ment to a Monograph of the Limniades," p. 3, as follows : "Am- 

 nicola, Q. & H. Head proboscidiform ; shell like Paludina, 

 opercule corneous and subspiral." No species was mentioned as 

 the type, or even as an example. Dr. Gould, in his celebrated 

 work, the " luvertebrata of Massachusetts," 1841, pages 228 and 

 229, gave a much more detailed description, pointing out other 

 important characters in which the genus is distinguished from 

 Viviparus, such as the production of the rostrum beyond the 

 foot, certain peculiarities in the habits of the animal, etc. He 

 states that " so far as observation has yet gone, the Amnicola is 

 oviparous, while the true Paludina is ovo-viviparous ;" and also 

 remarks that the tentacles are " frequently, if not always, unequal 

 in length; perhaps this is a sexual difference." The difference 

 in the length of the tentacles is, however, purely accidental. Dr. 

 Gould's description of the animal is excellent, though relating 



~^In some of the papers referred to below I find allusions to a work by 

 Mr Binney. As an excuse for not herein referring to such a work, I can 

 only say that I am unaware that Mr. B. has published anything whatever 

 upon the subject. I have, indeed, in common with some others interested 

 in the subject, received certain printer^s proof-sheets of a forthcoming work 

 on the Amnicol^e, Vivipari. etc., to be published by the Smithsonian Insti- 

 tution. The distribution of these proofs, with the view of eliciting addi- 

 tional information, speaks well for Mr. Binney's carefulness and strong 

 desire to perfect his work ; but we should no more quote publicly his un- 

 matured views, confidentially circulated in the form of proof, than we 

 should a private letter. 



V 



