44 TRACHELIPODA. TURRITELLA. 
Potamis cinctus. Plate V. fig. 36. Found in the upper 
marine formation at Headon Hill, and also in the same 
formation, Isle of Wight. 
This genus of fresh water shells is closely connected with Cerithium, differ- 
ing, however, in the epidermis being corneous, generally decollated ; the beak 
very short, and not recurved; in being destitute of a well defined canal ; but 
instead of it, a groove in the lip, in some species, and the aperture consider- 
ably shorter in proportion to its size than in Cerithium. Supposed to be a 
fresh water genus of shells. 
The genus consists entirely of fossil species, which seem to belong to the 
upper and lower fresh water formations; the London and Plastic Clay, &c. 
Genus XX XIX. — NERIN ZA, — Defrance. 
Generic Character. — Shell turreted, oblong, sub-canali- 
culated, with numerous volutions ; body large, but some- 
what contracted near the aperture ; aperture small, oblique, 
subquadrate ; columella provided with a strong fold, one on 
the inner lip, at the edge of the body volution, and one on 
the outer lip, which is thin. 
Nerinea Mose. Plate IV. fig. 88, Found in the 
Calcaire-grossier, Paris Basin. 
This genus is known only in a fossil state, and are peculiar to the Oolitic 
group of rocks, The prominent and large folds, on the superior angles of the 
aperture, distinguish it from all others. 
GRAND-DIVISION II. — PHYTIPHAGA. 
Animals destitute of a projecting syphon, and generally 
respure by an orifice; provided with jaws, and usually feed 
on vegetable substances ; shell with the aperture entire, being 
devoid of a notch or canal. 
TRIBE I.— TURBINACEA. 
Shell turreted, or conical, with an oblong or rounded aper- 
ture, and the margin disunited. 
Genus XL.— TURRITELLA. — Lamarck. 
Generic Character. — Shell turreted ; spire greatly elon- 
gated, consisting of many volutions ; body small in propor- 
tion to the spire ; aperture entire, orbicular, or sub-angulated ; 
its margin disunited above, but not reflected ; outer and 
inner lips with a slight sinus, situated generally near the 
upper parts, well marked in some species ; a more or less 
distinct sinus at the inferior and inner part of the lip, which 
is here very slightly reflected, but not turned back ; aper- 
ture furnished with a horny operculum. 
