FAMILY PERISTOMATA. 187 



Bythinia is an elegantly turbinated cone of five to seven smooth, 

 more or less rounded whorls of a semitransparent fulvous green 

 colour, covered by a thin horny epidermis. The aperture being 

 contracted at the upper, or, more strictly speaking, hinder, part, 

 has a pear-shaped tendency, with the margins continuous and 

 generally dark-edged. Sometimes the dark peristome of an imma- 

 ture aperture may be noticed across the penultimate whorls, in 

 adult specimens in the form of a varix. 



Dr. Gray notices the presence of a small veil on the right side of 

 the neck of Bythinia, and the Messrs. Adams speak of a small lobe, 

 but this appears to be an unimportant fold of the mantle, quite dis- 

 tinct from the tubular lobe in Paludina used for conveying the water 

 to the branchial chamber, and for the free development of which, 

 at the base of the tentacles, the eye is raised on a conjoined stalk. 



The Bythinice, which are now being examined by M. Frauenfeld, 

 of Vienna, the intelligent naturalist of the Austrian Novara expedi- 

 tion, have much the same distribution in both hemispheres as 

 Paludina. They are scattered, more or less sparingly, throughout 

 Europe, Asia, North Africa, and North America. The presence 

 of twelve species of Bythinia in France, is a tolerable indica- 

 tion of their being more plentifully diffused in Europe than has 

 been hitherto supposed. In Asia, there are three described by 

 G-erstfeldt from Siberia, and several have been collected in India, 

 China, and the Philippine Islands. In North Africa, Bythinia has 

 been collected in the tributaries of the Nile. In North America, 

 twenty-three species are recorded in Mr. Binney's ' Descriptive 

 Catalogue' of the Peristomata of that country, now passing through 

 the press, nineteen of which, having a spiral- whorled operculum, are 

 referred, in the proof-sheets he has been good enough to favour me 

 with, to Gould and Haldeman's genus Amnicola. 



The British Bythinice are : — 



1. similis. Shell very small, of five to six convex whorls chan- 



nelled at the sutures. Operculum horny, of two whorls, 

 nucleus lateral. 



2. tentaculata. Shell comparatively large, of five rather ventri- 



cose whorls. Operculum somewhat shelly, enlarged con- 

 centrically, nucleus central. 



3. Leachii. Shell smaller, of five scalariform whorls. Oper- 



culum somewhat shelly, enlarged concentrically, nucleus 

 central. 



