PILSBRY: NON-MARINE MOLLUSCA OF PATAGONIA. 553 



the group, but no type species seems to have been selected until William 

 Stimpson, in 1865, selected P. auberiana d'Orb. as type. 1 Bourguignat 

 in January, 1887, named P. acuta Drap. as type of the genus. 2 In 1895 

 Dr. von Ihering proposed to restrict Paludestrina to the group now called 

 Potamolithus, with P. peristomata as type. 3 This course cannot be fol- 

 lowed because of Bourguignat's earlier selection. P. acuta (Drap.) must 

 stand as the type of Paludestrina. 



The following names will fall as synonyms of Paludestrina : Littori- 

 nella Braun, 1846, type L. acuta (Drap.). Ecrobia Stimpson, 1865, type 

 Turbo minutus Totten. The preceding live in brackish water, or in 

 sheltered bays or estuaries, or sometimes where the water is fresh. 

 The exclusively fresh- water groups Bythinella Moq., 1851, type B. mridis 

 Moq., and Stimpsonia Clessin, i8y8, 4 type B. nickliniana (Lea), are in- 

 distinguishable from Paludestrina in shell, operculum and dentition, but 

 according to Moquin-Tandon the penis of B. ferrusma is bifid, while 

 that of P. minuta (Totten) was found to be simple by Stimpson. Until 

 the types of these proposed genera are studied and the forms of their 

 penes ascertained, there seems to be little reason for recognizing more 

 than one genus of these slender Amnicoloid snails in North America and 

 Europe, although it is likely that several may ultimately be defined. 



In Paludestrina (including Bythinella] the central tooth has a single 

 well-developed basal denticle on each side, but often a second one is 

 weakly developed. 



LlTTORIDINA HATCHERI Sp. nOV. 

 (Plate XLII, Figs. 7, 7 a, 8, 11-13.) 



The shell is minute, imperforate (though slightly rimate), rather solid, 

 olivaceous brown, smooth ; in shape ovate or somewhat pupiform. The 

 outlines of the spire are convex ; the summit minute, a little obtuse, 

 though the apex is not depressed. Whorls 4, convex, at first slowly, then 

 rapidly widening, the suture therefore descends more rapidly and 

 obliquely in its last volution, and it is also deeper than in those preceding. 



1 Researches upon the Hydrobiinas and allied forms, Smiths. Misc. Coll., No. 201, pp. 45,46. 

 This selection was not valid for the reason that auberiana was not one of the species included 

 in Paludestrina in d'Orbigny's original publication, but was added some years later. 



2 Etude sur les noms generiques des petites Paludinees a opercule spirescent, pp. 9, 10. 



3 Die Gattung Paludestrina, in Nachrichtsblatt d. d. Malak. Gesellschaft, XXVII, 1895, pp. 

 122-128. 



4 Malak. Blatter, XXV, 1878, p. 151. 



