2o6 Records of the Indian Museum. [Vol. XVI, 1919.] 



It was presented many years ago by Mr. F. J. Ede and is labelled 

 as being from a stream in Cachar. Two of the burrows completely 

 penetrate the block, one is incomplete and one has been cut open in 

 removing the mass. The entrance to all the burrows is oblique and 

 each has been commenced at a point at which the surface was 

 uneven or sloping. The calibre is even throughout and the 

 cross-section is narrowly lanceolate with a distinct notch at both 

 the broad and the narrow end. The height in a completed burrow 

 is 89 mm. and the greatest breadth 46 mm., the depth of the 

 lower notch about 8 mm. The inner surface is smooth except for 

 a number of shallow but rather broad longitudinal grooves on the 

 sides. 



If the shell removed from the burrow be examined it will be 

 found to resemble it closely in cross-section but to be a little 

 smaller in all directions, and coarse longitudinal ridges on its 

 surface will be noted corresponding roughly with the grooves on 

 the wall. There is no possibility of the excavation having been 

 made by the rotation of a body of the size and shape of the shell, and 

 it is evident from a comparison of old and young specimens that 

 the instrument used must be the anterior margin of the valves, 

 which is worn and smoothed in old shells. 



In young shells the anterior region differs considerably in 

 shape from that in old shells and has distinctly the appearance of 

 a cutting tool. The valves are strongly compressed, their margin 

 is very sharp and the curvature is of a convenient type. 



The foot ^ of Solenaia resembles that of Physunio ^ in shape 

 but is considerably more elongate. As I have recently shown' 

 the latter form makes its way through mud with the shell in a 

 vertical position and with a swaying motion, by alternately pro- 

 truding and retracting the foot, and I believe that Solenaia cuts 

 its way into the rock in a similar manner. Having found a suitable 

 spot where the surface is irregular or shelved, it applies the 

 anterior end of its shell to the surface and by alternately thrusting 

 out and drawing in its foot moves the sharp margin up and down 

 against the rock, thus cutting a groove into which it thrusts itself. 

 The movement is probably complicated by a laterally swaying 

 motion and the coarse ridges on the shell assist in enlarging the 

 aperture. A great deal of the excavated matter must be taken 

 into the mantle cavity and expelled in the manner indicated by 

 Mr. Ede. 



' Ekendranath Ghosh, Rec. Ind. Mus. XV, p. ni, pi. xvi, fig. 2 (1918). 



2 Id., ibid., fig. 3. See also Baini Prashad, Rec. Ind. Mus. XIV, pi. xxii, 

 fig. I (1918). 



3 Annandale, Rec. Ind. Mtis. XIV, p. 141 (1918). 



