494 Mr. W. H. Benson on new species of Paludomus. 



XLVII. — Descriptions of three new species of Paludomus froju 

 Burmah, and of some forms of Stenothyra (Nematura) from 

 Penang, Merguij ^c. By W. H. Benson, Esq. 



The forms first to be described belong to the genus Paludomus 

 proper of Swainson (recently deceased at New Zealand), who was 

 unacquainted with the Cingalese forms added by Reeve, and since 

 separated chiefly with reference to the opercula. This circum- 

 stance, and not the applicability of Reeve's character, which is 

 far from expressing the true features of the operculum, properly 

 warrant Mr. E. Layard's restriction of Swainson's name to the 

 shells which present a close affinity to P. conica, Gray. In a 

 paper contained in the Proc. Zool. Soc. for 1854, Mr. Layard 

 stated that, with the addition of the position of the nucleus in 

 the operculum. Reeve's characters sufficiently describe it ; but, 

 even thus amended, the author has omitted the essential cha- 

 racter separating it from Paludina, as pointed out to him in a 

 communication dated in April 1852, when I accompanied the 

 information with the distinctive characters of the divisions 

 Tanalia, Gray, and Philopotamis, Lay., under the names of 

 Serenia and Heteropoma, and with figures of the opercula of the 

 three genera. The fact is that the nucleus of Paludomus proper, 

 unlike that of the similarly horny and concentrically striate 

 operculum of Paludina, is subspiral, and analogous to the testa- 

 ceous one of Bithinia. I had prepared a memoir on the subject, 

 with illustrations of the variations of the opercula in Paludomus 

 and the Melaniada, which has been partly anticipated by the 

 paper already before the public. 



The genus Paludomus requires revision, especially with respect 

 to the unfigured species, which demand more strictly defined 

 characters. It will be found also that several species belong to 

 it, of which the affinity was unsuspected by the describers ; 

 among them Melania obesa^ Philippi, which is really an inha- 

 bitant of the vicinity of Bombay, not of Australia, and which 

 may possibly be the same as P. parva, Layard ; then the Egyp- 

 tian Cyclostoma BulimoideSy Olivier, which has the true typical 

 operculum of Paludomus, and which is singular in the genus 

 from presenting a perforated base; lastly, Melania lutosa of 

 Souleyet from the lower part of the Hooghly River near Cal- 

 cutta. Both Philippi and Souleyet notice the concentric stria- 

 tion of the operculum in the shells which they doubtfully referred 

 to Melania, overlooking however the structure of the nucleus. 

 In the Atlas to the ' Voyage of the Bonite,' Souleyet gives a figure 

 of the animal, which curiously illustrates its affinity to both 

 Melania and Paludina. 



The ungulate operculum of Tanalia, Gr., is analogous to that 



