28 PALUDJNID^, 



are oviparous, instead of ovoviviparous ; their eyes are 

 not placed on pedicles, or foot-stalks, but are sessile ; 

 the operculum is testaceous, instead of horny, and 

 its nucleus is nearly central ; the right tentacle of 

 the male is of the same size as the left. Gwyn 

 Jeffreys very justly remarks that "although the de- 

 rivation of the word Bythinia would imply that these 

 molluscs inhabit deeper water than others of the 

 same family, such is not the case ; they generally 

 frequent small streams, canals, shallow ponds, and 

 ditches."— ^.C, vol. i. p. 59. 



They breed from May till August, and the eggs, 

 which vary in number from ten to seventy, are de- 

 posited on stones or aquatic plants, in three, or more 

 rarely in two rows, which form a transparent band. 

 The fry are excluded at the end of from twenty to 

 twenty-five days, and attain their full growth in about 

 two years. 



I. Bythinia tentacula'ta,* Linn£. Pl. IV. 



Body black or dark brown above, dirty grey beneath ; head 

 small, semi-oval ; te7itacles filiform, considerably diverging ; eyes 

 prominent, somewhat oval, black; month with a reddish margin ; 

 foot much broader than the snout, rounded in front, nearly 

 opaque, edges greyish ; tail bluntly rounded at its extremity, 

 half hidden by the operculum. 



Shell conical, moderately solid, rather glossy, semitransparent, 

 yellowish or brownish horn-colour ; closely and finely striate in 

 the line of growth and microscopically so in a spiral direction ; 

 epidenuis thin ; whorls 5-6, convex, body whorl occupying 

 rather more than one-half of the length of the shell, apex some- 

 what sharply pointed ; suture oblique, rather deep ; vwtith oval, 

 angulated above ; outer lip thick, and frequently furnished in- 



* Provided with tentacles. 



