n INTRODUCTORY. 



factorily a single species of our fluviatile univalves, one must 

 have before bim a very large suite of specimens of all ages from 

 every portion of the district which it inhabits, as well as authen- 

 tic specimens of every allied described species, with an equally 

 complete suite of individuals of them. Add to this knowledge 

 sufficient to obtain any additional light from the anatomy of the 

 animal, and he may be in a position to speak authoritatively in 

 regard to its specific characters, its relations to other species, its 

 variations, geographical distribution, synonymy, &c. 



Not possessing these requisites, I have not attempted to pre- 

 pare a complete monograph, but rather a report on the present 

 state of our knowledge of the subject. I have given an English 

 translation of all the original descriptions, and a fac-simile of 

 the outline of each original figure. I am in hopes my work will 

 conduce to a more perfect knowledge of the various families, by 

 furnishing a basis for future research. 



Although I do not consider myself competent to settle defi- 

 nitely many questions of synonymy, my opportunities have been 

 ample to decide some. In the genera Ampullaria, Valvata, and 

 Amnicola, I have adopted almost all the published descriptions, 

 having but little opportunity of comparison of species, or of gain- 

 ing information, other than that furnished by Haldeman. In the 

 genus Vivipara, I have had better means of making correct deci- 

 sions. Before studying any descriptions, or, indeed, paying atten- 

 tion to any specific names, I had before me over 90 diiferent lots, 

 containing 320 specimens, exclusive of duplicates, belonging to 

 the Smithsonian Collection, and which had never been assorted 

 or determined. To these I added the specimens figured by Prof. 

 Haldeman in his Monograph, which he has since presented to the 

 Academy of Natural Sciences of Philadelphia. Dr. James 

 Lewis, of Mohawk, very kindly added all his specimens of the 

 genus ; Mr. J. G. Anthony all his types, and numerous other 

 interesting specimens ; Dr. E. R. Showalter, of Uniontown, 

 Alabama, furnished me with many southern species, in large 

 numbers, of every stage of growth, and from the Philadelphia 

 Academy, I borrowed all their specimens, including Say's types. 

 In addition to the gentlemen already mentioned, I am indebted 

 to the kindness of Mr. Lea for constant access to his extensive 

 collection, the study of his types, with privilege of having them 

 drawn, and much of his valuable time. After having studied the 



