igig.] N. ANNANDAI.K& B. Prashad : Gangetic Delta Molluscs. 251 



tooth interpolated between the two laterals on either side ; the den- 

 tal formula thus being 1.3 1.3.1. instead of 12 1.2.1. (6) The central 

 tooth is quadrangular and broadly transverse ; it has three stout 

 subequal cusps and a pair of extremely large denticulations 

 arranged side by side at each side of its base, (c) The denticula- 

 tion of both the lateral teeth is very coarse but short, {d) That 

 of the marginal tooth is similar to and intermediate between that 

 of .4. hrevicula and A. heddomiana \ there is besides on the outer 

 margin of the tooth a peculiar pointed, but' apparently membran- 

 ous process. 



It is possible that this species may have ultimately to be 

 recognized as a distinct genus, but we have no information as to 

 the radular characters of the typical species of Cyclotrophis— 

 C. papiiemis (Albts.), which was found on the south coast of New 

 Guinea. As we have shown above, those of the Chinese A . violacea, 

 which would be assigned to this group on shell characters alone, are 

 quite different from those of A. francesiae. 



Family MELANIIDAE. 



Genus Melania, Lam. 



vSub-genus Mainwaringia, Nevill. 



1886. Maimvariiigia, Nevill, Haud-List Moll. Iiid. Miis., II, p. 28O. 



Although Nevill refers to the only known species as a " new 

 generic type," he places it as a sub- genus of Melania, a view with 



1 KXTKiG. 5. — Kadular tecih of Mainivari ngia pulmloiuideti, Ne\ill. 

 {a) Teeth viewed from above. (b) Lateral view of marginal tooth. 



which we agree. His statement that it is intermediate between 

 that genus and Paludomus seems to be based on the form of the 

 operculum, and perhaps on the consistency of the shell. Both 

 Blanford,' however, and the vSarasins* have shown from different 

 points of view that the former can hardly be regarded as of great 

 generic importance in the Melaniidae. The form of the shell 

 differs little from that of Melania, and we are of the opinion 



' Trans. Linn. Soc, XXIV, pp. 166-167 (1864J. 



2 Die Si(ss7vnsser Mollusken von Celebes, pp. 5-9 (1898). 



