SNAILS AND LIMPETS. 171 



ment, upon the sides of tlie aqTiarium. The labour of 

 laying the eggs, sometimes numbering as many as seventy, 

 occupies several days. The little animal carefully cleans 

 every spot upon which she deposits an egg. The fry ai-e 

 hatched, according to the temperature of the water, in from 

 twenty to twenty-five days, and do not reach maturity until 

 they are about two years old. The body of the animal is 

 almost black, and spotted with yellow. The tentacles are 

 filiform (thread-like), and diverge considerably ; both tentacles 

 of the male, unlike the genus just described, are of the 

 same size. The eyes are black, large, and sessile. The shell 

 is conical, and of a yellowish horn-colour and glossy. 

 There are five whorls, the last taking up more than half 

 of the shell. The sutures are 

 rather deep, and the apex is 

 pointed. The operculum is thick 

 and oval. This is a useful little 

 snail in the aquarium, often 

 feeding upon decaying vegeta- 

 tion, and not unwilling at times 

 to partake of a little animal 



food. From the name Bythinia '^°- ^^^- B™""* tentaculata. 

 one would imagine that the 



members of this genus always dwell in deep water; but this 

 is not the case by any means, for they are frequently found 

 in shallow streams, small ponds, canals, and ditches. 



Valvata piscinalis is a little mollusc, whose name signifies 

 that it possesses an operculum and lives in fish-ponds : it 

 should not be introduced into an aquarium which is rather 

 wanting in growing plants, for it wiU feed chiefly upon 

 them. It is an interesting animal and well worthy of a 

 place in a tank which is rich enough in vegetation to 

 supply it with food without suffering in consequence. The 

 respiratory organs of this snail ai-e curious : it possesses a 

 branchial plume and a branchial thread. The former 

 consists of gUls which somewhat resemble feathers, and 

 which extend beyond the edge of the mantle when the 

 animal is in motion. The latter is a tentacle-like appendage . 



