242 Records of the Indian Museum. [Voi,. XVI, 



This genus seems to us to be well characterized l:)y the follow- 

 ing features : — 



(i) The spire is vestigial, but distinctly lateral and spiral. 



(ii) The shell has no wing-like lateral projections. 



(iii) The columellar plate extends as a transverse septum 

 along the aperture of the shell for at least half its length. 



(iv) The operculum is semicircular and completely exposed. 



Preston {op. cit.) includes species of Dostia in Septaria, Fer,, 

 but this genus differs in the still more reduced spire, which is 

 hardly coiled and does not project at its base beyond the body- 

 whorl ; in its much narrower columellar plate, and specially in the 

 fact that the operculum, which is nearly square, is concealed in 

 the muscles of the foot. 



We are convinced by a study of specimens from a number of 

 different localities that at least three distinct species can be dis- 

 tinguished in the Gangetic Delta alone, and that none of these are 

 synonymous with the true D. violacea (Gmelin). Two of these 

 species have already been described by Benson, but we can find 

 no record of any form with which the third can be identified. 



Dostia cornucopia (Benson). 

 (Plate XX, fig. 2a). 



1836. Neretina cornucopia, Benson, Jou;-n. Asiat. Soc. Bengal, \ , p. 748. 

 1867. Neretina (Dostia) cornucopia, Blanford, Ibid., XXXVI, pi. 2, 

 p. 60, pi. xii, fig's. 23-25. 



In this species the shell is relatively large, porcellaneous, thin 

 and high. The columellar plate extends very little more than half 

 way across the true mouth of the shell, i.e. the part occupied by 

 the operculum when the soft parts are retracted. The peri- 

 ostracum is pale olivaceous, sometimes with well-defined transverse, 

 zig-zag black lines. The coUumellar plate is blackish and there is 

 a blackish margin to the true mouth of the shell. 



The difi'erences between shells from the Irrawady Delta and 

 those from that of the Ganges noted b}^ Blanford are not constant. 



The operculuni is relatively short, its breadth being two-thirds 

 of its length. The lateral projection is stout and blunt, but of 

 considerable length. Its distinctive features in other respects can 

 be seen from our figures. 



We have examined specimens of this species from the upper 

 part of the Gangetic Delta, from that of the Irrav/ady, from the 

 Patani river on the east coast of the Malay Peninsula and from 

 Cochin-China. 



Blanford says that in the Irrawady Delta D. cornucopia is 

 usually found on tree-trunks covered at high-tide by brackish 

 water. In the delta of the Ganges, however, it seems to occur 

 chiefly, if not exclusively, at the edge of creeks of fresh or almost 

 fresh water near the upper limits of tidal influence. The species 

 is, however, scarce in Bengal. 



