30 THE NAUTILUS. 



east over New England and Canada, and as far west as Indiana and 

 Michigan. "West of the Alleghanies it gradually gives way to P. 

 sayii Tappan. I have never seen a well authenticated example 

 west of the Mississippi or south of the Ohio. 



( To be continued.} 



THE SYNONYMY OF BYTHINELLA OBTUSA LEA. 



BY BRYANT WALKER. 



This well-known and characteristic little species, which has an 

 extended range through the Northern States from New York to 

 Iowa, if not further west, was first described by Lea, in 1841, as 

 Pahidina obtusa. Haldeman, in his "Monograph of the Fresh-water 

 Univalve Mollusca" (1844?), although apparently unacquainted 

 with the species, referred it to the genus Amnicola. Binney (1862), 

 in his preliminary study of the fresh-water operculates, also placed it 

 among the Amnicola. Stimpson (1865), in his "Researches upon 

 the Hydrobiinre," considered it " probably referable " to Bythinella. 

 In this he was followed by Binney (1865) and Tryon (1870), and 

 from that time the species has been uniformly known and cited as 

 Bythinella obtitsa. 



Unfortunately, however, Lea had been anticipated in the use 

 of the name, Pahidina obtusa, by Troschel, who, in 1837, had de- 

 scribed a species of Vivipara from Bengal under that name. It 

 follows necessarily, therefore, that Lea's name will have to give way; 

 and had not the species already been described by another author 

 under a different name, a new one would have to be provided for it. 



Were it not for the express statement that his species was imper- 

 forate, I should be inclined to refer this species to Green's Pahidina 

 alleghaniensis (see Binney, L. & F. W. Shells, III, p. 60), which 

 has several years' priority. The differences relied upon by Lea in 

 differentiating his " obtusa " would scarcely be sufficient in the ab- 

 sence of the other peculiarity. I know of no other species from 

 Pennsylvania that would fill the description except Amnicola decisa 

 Hald., which might well be called imperforate. On the other hand, 



