G. O. SABS. 



the size of the larger variety, described by Baird, according to 

 the small line subjoined to the figure. Brady, on the other 

 hand, gives the length of his Ceylon specimens as V12 of an 

 inch, or about 2,10 mm. 



The shell is very elongated and narrow, approaching the 

 cylindric form, though rather compressed. Seen laterally (PI. I, 

 fig. 7) it exhibits a somewhat reniform shape, the height being 

 nearly the same throughout the greater part and considerably 

 less than half the length, or more precisely equalling about 2 /s 

 of the same. Both extremities are rounded and almost of the 

 same appearance, or the posterior a little lower. The dorsal 

 margin is much flattened and nearly quite straight in the 

 middle, sloping in front and behind rather abruptly to the 

 corresponding extremity. The ventral margin is distinctly sinu- 

 ated a little in front of the middle and joins the anterior and 

 posterior edges by a quite even curve. Seen from above or 

 below (fig. 8) the shell exhibits a very narrow oblong form, the 

 greatest width not even attaining y B of the length. The 

 lateral contours are very little if at all curved in the middle, 

 nearly parallel, and both extremities subacuminate, the anterior, 

 however, somewhat narrower than the posterior. The surface 

 of the shell is smooth and polished, beset with scattered fine 

 hairs, as usually, more distinct at both extremities. 



The valves are of rather firm consistency, though very 

 pellucid, and are nearly equal, or the left very little longer 

 than the right. The free marginal part (see PL V, fig. 1) is 

 highly chitinised and without any such pellucid border, as in the 

 preceding genus. On the other hand, it exhibits throughout a 

 very marked transverse striation, the stripes having the appear- 

 ance of somewhat irregular grooves, terminating at a short 

 distance from the edge and generally each giving origine to a 

 marginal hair. These stripes become on the upper part of the 

 anterior extremity very elongate and somewhat converging 

 inwards. In not yet fully developed, though still rather large 

 specimens the edges of the valves are much less chitinised and 

 without any trace of the above described peculiar transverse 



