du genre Hydrohia et des genres voisins, p. 133*) only proposed 

 nominally in 1821 (Sturm Beutsch. Fauna, Heft 5, p. 46), 

 without any generic definition ; and this name was followed 

 by three other specific names, without authors, viz. : — 

 Hydrohia acuta, H. vitrea, and H. minuta. Of these the first 

 is a saltwater species, the second freshwater, and the third, 

 says Mons. Fischer, is unknown. The idea of Hartmann 

 was (says Mons. Fischer) to separate Faludince with spiral 

 opercula from those of concentric structure, which is the 

 division of VivijJara and Bythinia of authors. 



The same author di-aws attention to the fact, with regard 

 to Faliidestrina, that Mons. D'Oibigny says expressly that 

 he intended his genus to apply to marine and freshwater 

 species, but that it included all the marine Faludince ; so 

 that Faludestrina became exactly synonymous with Hydrohia. 

 It is probable that the only definition of Hartmann for the 

 latter genus was that it was intended for Faludince with an 

 elongate and acute spire. Subsequently he regarded it only 

 as a sub-genus of Faludina. (1840. Syst. Uehers, ita Her- 

 man^isen loc. cit.) 



Dr. P. P. Carpenter, in his most careful and elaborate 

 Catalogue of Mazatlan Shells, which is one of the British 

 Museum catalogues, at page 30 has the following references : 

 — G-enus Hydrohia, Hart, ut supra Fltll. Hand. Conch. Leachia, 

 Fisso, 1826. Fcdudinella, Loven, (! Fcdudinella, Pfeifferf) 

 Dr. Car2>eiiter then remarks — and the observation is one 

 which bears in an important manner on the subject of this 

 paper — that the Mazatlan shells of HydrcMa ulvce, after care- 

 ful microscopic examination, are not seen to have the slightest 

 specific variation from the British specimens, and it did not 

 seem allowable to impose on them a new name merely from 

 geograj)hic considerations. Mr. J. E. Gray, in his Guide to 

 the Systematic Bist. of Moll. (British Museum catalogues) 

 J). 89, says of Lithoglyphus that Dr. Philippi has placed that 

 genus, and Hydrohia with spiral opercula, as sub-genera of 

 Faludina ; but Faludomus with annular opercula he places as 

 a sub-genus of Melcmia.X Mr. Gray does not define Hydrohia 

 in the way adopted by Messrs. Adams, in their Genera of 

 Becent Mollusca, though they both distinguish Lithoglyphus 

 from that genus, and reject Faludestrina. 



* This paper was written, but not published, before Mons. 

 Fischer's article reached me. In consequence I have revised the 

 whole of my MS., as the additional information it suppHed was new 

 and valuable, though our conclusions, formed independently, were 

 nearly identical. 



t This can hardly be, as Pfeiffer sustains the name Lithoghjpims. 



X)p. 1G7 and 1G8. 



