AND ALLIED FORMS. 5 



The above mentioned characters may be tabulated as follows : 



A. Operculum concentric ....... Bvthinux^. 



B. Operculum spiral. 



a. Operculum pauci-spiral Skenein^e. 



b. Operculum subspiral. 



1. Operculum with an internal process , . RissoiNiNiE. 



2. Operculum without an internal process. 



* Foot without lateral sinuses. 



t Rhachidian tooth of the lingual ribbon 

 with the basal denticles on the infe- 

 rior margin RissoiN^. 



tt Rhacliidian tooth of the lingual ribbon 

 with the basal denticles on the ante- 

 rior surface behind the lateral mar- 

 gins ...... Hydrobiin^. 



** Foot with lateral sinuses .... Pomatiopsin.b. 



It is with the two subfamilies last mentioned that we have to do 

 in the pi'esent paper : the Hydrobiin^i: and Pomatiopsin^. 



I adopt, for several reasons, the name Hydrobiinse for the 

 first of these subfamilies in preference to that of Amnicolinte, 

 proposed by Mr. Gill^ for a part of the group, to which some Poma- 

 tiopsinae were added. First, because the group was first indicated 

 by Troschel,^ under the name Hydrobife ; next, because the first 

 genus of the subfamily ever described was called Hydrohia ; and 

 lastly, because the name Amnicolinae is not universally applicable, 

 since these animals are not all inhabitants of rivers, or even of 

 fresh-water, some of them living in shallow inlets of the sea. The 

 name Hydrobiinae is in every respect appropriate. 



J. D. W. Hartmann was the first to separate the.se little snails 

 from the old heterogeneous group called Paludina. According 

 to Herrmannsen^ he published the genus Hydrohia in 1821, in 

 Sturm's "Fauna Deutschlands," Abth. YI, Heft 5, p. 46. I have 

 been unable to find and consult this work for the purpose of ascer- 

 taining the type of the genus, but the author doubtless intended 

 to include in it both fresh-water and marine forms, certainly fresh- 

 water ones, as he again used the generic name {fide Herrmann- 

 sen) in a treatise on the land and fresh-water shells of Switzer- 

 land, in Steinmuller's " Neue Alpina," I, 258. Moquin-Tandon* 



' Proc. Acad. Nat. Sci. Philad., 1863, p. 34. 

 2 Gebiss der Scbnecken, I, 106 (1857). 

 ^ Ind. Generum Malacozoorum, I, 545. 



* Hist. Nat. des Moll. ter. et fluv. de France, II, 514. 



