386 On Indian and Burmese Species of Assiminea. 



a brackish-water genus, living between tide-marks on the mud 

 of estuaries. But species are to be found both in perfectly salt 

 and in perfectly fresh water. The water of Bombay harbour is 

 almost purely sea-water ; and I have met with some of the Bom- 

 bay species on the sea-shore at Bombay, far from the mouth of 

 the harbour : on the other hand, the water of the Hoogly, where 

 A. Francisci is found, is quite fresh. The latter species occurs 

 also in brackish water, I believe ; for, although I have not noticed 

 it alive, dead shells are common in the brackish-water creeks 

 east of Calcutta. The individuals that have been habituated to 

 salt water, however, will not live in fresh, nor vice versa. In 

 Dr. Leith's description of Optediceros, he says of the animals 

 generally : — " If put into salt water, they all quickly make their 

 escape from it by creeping up the sides of the vessel ; but if 

 placed in fresh water, they close their opercula, and remain shut 

 up until they die.^' I tried a similar experiment with A. Fran- 

 cisci, from the fresh water of the Hoogly. On placing the spe- 

 cimens in perfectly fresh water from a tank, all crawled out of 

 the water; but on putting them in brackish water (not salt 

 water), a few began to crawl about, but by degrees nearly all 

 closed their opercula and remained at the bottom ; and after half 

 an hour only six out of about two hundred specimens had crawled 

 out of the water. On throwing away the brackish water, and 

 substituting fresh, all began moving about and creeping out of 

 the water as usual. . 4. 



(^ 



Fig. 1. Assiminea cnruea, Leitli. 



Fig. 2. A. subconica, Leith. 



Fig. 3. A. marginuta, Leith (type). 



Calcutta, October ISGO*. 



Fig. 4. A. mnrginata, var. major. 

 Fig. 5. A. rotunda, Fairbank. 

 Fig. (). A. rubella, W. Blanford. 



