BITHINIA. 25 



inner surface of the respiratory cavity; the 

 ridges narrow, slightly dilated, and angulated 

 near the middle. (Moquin Tandon, t. 39. f. 31. 

 32.) Stomach with cartilaginous stylets. Male 

 organs at the hinder base of the right tentacle, 

 always exposed, filiform, bifid. (Moquin Tan- 

 don, t. 39. f. 37.) Shell spiral; mouth oval, 

 entire; peristome thickened. Operculum an- 

 nular, with an internal shelly coat; crabby 

 claws, not withdrawn in the aperture of the 

 shell. Oviparous, eggs in oblong masses. 



1. BITHINIA Gray. (Bithinia.) 



Operculum filling the mouth of the shell, lined 

 internally with a thick shelly coat ; nucleus 

 subcentral (f. 4. c.) ; the mouth of the shell 

 ovate, continued, rather angular behind, with 

 a slightly thickened internal rib. 



Fig. 4. These animals are 



oviparous, their eggs 

 being deposited in 

 oblong groups, like 



Bithinia ventricosa. the LimiKBl Or Pond 



c ; operculum. Smu\&, Qn the gtemg 



and leaves of fresh- water plants. (See Pfeiffer, 

 Moll t. 6. f. 10, 11, 12.) 



M. Moquin Tandon erroneously considers the Hy- 

 drobia of Hartmann, which has a subspiral horny 

 operculum, as a sub-genus of Bithinia, under the 

 name of Bythinella, and gives the name Elona to 

 the true Bithinice. 



