24 
BITHINIAD^. 
1, Littorhsta anatina. 
Pallid in a anatina. Drap.^ Michaud^ Alder ^ Mag. Zool. and 
Bot. 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 AlgcB. 
2. Littokina muriaticay 
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 uIvcb. Hart- 
mann has formed a genus called Hydrobia from these 
small Littorinse. 
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 
right side. Gills single, in the form of a trans- 
verse parallel, flexuous plaits attached to the 
