146 Records of the Indian Museum. [Vol. XXII, 



On a careful comparison of Preston's unique type with the 

 other specimens in the Indian Museum I find that it is only a 

 half-grown shell of B. similis, Prime. It is not possible to be 

 quite definite as to the validity of B inflata, Prime, as a species 

 distinct from B. similis ; it will probably, when larger series are 

 a\-ailable, have to be considered as only a varietj' of B. similis, 

 but for the present I have not adopted this course. Both the 

 species belong to the group Ellipticae of von Martens' classifica- 

 tion. In this group the shell is elongated in an antero-posterior 

 direction, the ventral border is only slightly arched and the shells 

 have no radial sculpture. 



Within the limits of British India, Burma and Ceylon, the 

 genus Batissa is known to occur in the Andaman and Nicobar 

 Islands only and has not so far been found on the mainland. 



Soft parts. — The following description of the soft parts is 

 based on the Celebes specimen sent to me by Prof. Max Weber 

 and may be considered as a supplement to the short description of 

 the animal in von Martens' paper cited above. 



Corresponding to the shape of the shell the animal is trigonal- 

 elliptical, and is not much swollen in the umbonal region. The 

 specimen preserved in spirit is of a deep yellowish brown colour, 

 the palps and the gills being somewhat greyish. 



The mantle is comparatively thicker than in the genus Corbi- 

 cula or in Villorita, but the free region below the pallial line is 

 not definitely marked off as in those genera, owing to the radial 

 muscle fibres being not very thick and distinct even though they 

 are well developed. The margin of the mantle is entire and 

 bears a continuous row of small conical papillae on the inner sur- 

 face slightly internal to the edge as in Villorita, but the papillae 

 all along are not of the same size as in Villorita. The condition 

 is intermediate between that found in Corbicula in which they are 

 absent in the pedal region and that in Villorita where they are 

 approximately the same size all along 



The arrangement of the siphonal and pedal orifices is similar to 

 that in the genera Corbicula and Villorita, but the limits of the two 

 are different. The pedal orifice is limited anteriorly by the ven- 

 tral margin of the thick anterior adductor muscle and is separated 

 from the siphonal orifice by a long connection, about half an inch 

 long, of the mantle flaps of the two sides with one another in 

 fine with the posterior side of the foot ; in this region of union 

 also the papillae of the mantle are present in two rows along the 

 line of union. The siphonal orifice is rather extensive extending 

 above to very nearly the upper margin of the posterior adductor 

 muscle. The mantle is not externally notched to mark off the 

 regions for the two siphonal apertures. 



Of the adductor muscles, the posterior is much larger than 

 the anterior and both are nearl}' subquadrate in outline. The 

 pallial muscle-fibres have already been mentioned, in these the 

 siphonal retractors are not distinctly indicated. 



The two siphons are fully contracted, but appear capable of 



