24 BITHINIAD^. 



1. LiTTOElNA anatina. 



Paludina anatina. Drop., Michaud, Alder, Mag. Zool. and 

 Sot. ii. 116. — Bithynia inflata. Leach, Syn. Moll. 210. 



Sometimes found in the marshes at Greenwich, 

 with the Assiminia Grayana. The shell is ovate, 

 perforated, thin, transparent; the whorls are ven- 

 tricose, rounded, and the mouth ovate ; the operculum 

 is horny, brown. It is like Bithinia ventricosa, but 

 smaller and shorter, and has a horny spiral opercu- 

 lum, like the periwinkle ; the peristome is continued ; 

 the shell is often covered with green Algce. 



2. LiTTOElNA muriatica, 



Turbo muriaticus, Linn. — Cyclostoma acutum, Drap. 



which has been placed by the latter author as a 

 fresh-water species, is abundant on many parts of our 

 coasts. It is nearly allied to Littorina ulvce. Hart- 

 mann has formed a genus called llydrohia from these 

 small Littorinas. 



Fam. 3. BITHINIAD^. 



Head annulated, contractile, narrow, and not ex- 

 tending to the plane of the foot. Teeth in 7 

 longitudinal series, the lateral converging. 

 {Moquin, t. 39. f 26. 28.) Jaws none. Ten- 

 tacles subulate, equal. Eyes sessile, on the 

 outside of the base of the tentacles. Mantle 

 simple in front; neck with small veil on the 

 rio-ht side. Gills single, in the form of a trans- 

 verse parallel, flexuous plaits attached to the 



