I9I9-J N. Annandale & B. Prashad : Gangetic Delta Molluscs. 255 



the anterior fold intermediate. The columellar callus is well 

 developed. The surface of the shell is polished, shining and some- 

 what opalescent, but is partly covered by a thin blackish-brown 

 deposit. There are two fine but clear-cut spiral ridges on the 

 whorls of the spire, extending on to the upper part of the body- 

 whorl, the central region of which is quite smooth. At the base 

 of the body-whorl there are five other still finer spiral ridges, 

 which are more closely approximated behind than in front. 



Measurements of type-shell {in millimetres). 



Length . . . . . . . . 3-25 



Breadth of body-whorl . . . . 2*0 



Breadth of spire at base (dorsal view) . . i*o 



Length of spire (dorsal view) . . . . i"o 



Length of aperture . . . . . . 2*2 



Breadth of aperture . . . . . . o'5 



The living animal is devoid of external pigment and is of 

 much the same shade as the shell. There are no e3-es. The 

 foot is relatively small, broadly rounded behind, expanding in 

 front into a flattened, bluntly pointed almost triangular process 

 on each side. The cephalic disc is large and extends over the 

 anterior part and the lateral margins of the shell ; in front it is 

 notched in the middle Hne, and it is expanded at each side into 

 a broad flattened process like that of the foot, but larger ; the 

 posterior margin is nearly straight, but folded in the middle line 

 in such a wa}' as to form an incomplete siphon, which, however, 

 hardly projects at all. 



TyPe-specimen : M ' ^;|''' in the collection of the Zoological 

 Surve}'^ of India. 



Locality. — Creek at Kaikal Maree, near Port Canning, Gan- 

 getic Delta, from a muddy bottom in 4-6 fathoms : specific gravity 

 of water (reduced to i5°C) i"oi725. 



The shell resembles that of R. apicata, Nevill, in some res- 

 pects, but is larger and has the body-whorl much broader, the 

 mouth more contracted and the lateral callus much more strongly 

 developed. 



The animal differs from that of R. auriculata as figured by 

 Fischer {Man. Conch., p. 36, fig. 322, 1887) in being devoid of 

 ej'Cs, in the different shape of its foot and cephalic disc, and in 

 its much less well-developed cephalic siphon. 



Family AURICULIDAE. 



Genus Auricula, Lam. 



At least three species of this genus, to which we give a some- 

 what broad application, occur commonly in the lower parts of the 

 Gangetic Delta, namely — A. auris-judae, Lam,, A. gangetica, 

 Benson, and the form we describe below. Benson. Stoliczka and 



