SNAILS AND LIMPETS. 169 



being hatched within the oviduct of the mother, and the fry 

 are retained there, sometimes for at least two months, until 

 they are able to take some care of themselves. The young are 

 not excluded from the parental sheU all at once, but gradually. 

 Sometimes only two or three are sent out into the watery 

 world around them in the course of a day or longer. These 

 fry, frequently numbering as many as thirty, have at first 

 rows of bristles or cilia upon their shells, which after a time 

 disappear and are replaced by the brown bands which mark 

 the full-grown snail. P. contecta has long and elegant 

 tentacles, which diverge somewhat. The eyes, which are 

 roimd and black, and rather large, are situated upon short 

 pedicels on the outer bases of the tentacles. The colour of 

 the body varies from dark grey to dark brown, and is spotted 

 with yellow. The foot is ovate, and has a yellowish margin; 

 the head is small. The brownish- green shell is sometimes 

 IJin. long, and more than lin. broad. There are six whorls : 

 the first is not much more than a mere point, but the last is 

 very large, exceeding in length half of the entire shell. The 

 last whorl has three, and the two whorls next to it two, 

 rather broad brown spiral bands. The sutures of the shell 

 are very deep, and the aperture is pear-shaped. The oper- 

 culum is thin, and the lines of growth are plainly seen. This 

 snail is very usefiil in the aquarium. The male has the right 

 tentacle shorter and thicker than the left. 



Paludina vivipara (Fig. 116) very much resembles the last 

 species in habits, habitat, and structure. The body, in colour, 

 is almost black and spotted with yellow ; the tentacles are 

 bluish-black and are thinly sprinkled with yellow or orange 

 spots ; the shell is much like that of the P. contecta, but it 

 is more oblong in shape and less glossy in colom-, and the 

 whorls are not so swollen, nor consequently are the sutui'es 

 so deep. The body-whorl of this snail has three bands, and 

 not four, as represented in the illustration. The shells of 

 both species are marked with broad brown bands, almost 

 exactly in the same way. The apex of the shell of P. 

 vivipara is blunter than that of the P. contecta, and the 

 operculum thicker. This snail, which is sometimes called the 



