EUOMPHALUS. TRACHELIPODA. 49 
very slightly produced above; concave below ; aperture 
ovate ; edges of the outer lip acute, and very slightly re- 
flected. Destitute of an operculum. 
Planaria nitens. Plate VI. fig. 19. 
This genus strongly resembles Planorbis, but the species are marine. We 
are only acquainted with two in a recent state, which were found in the Frith 
of Forth, near Dunbar. 
One fossil species, the nitens, has been found in North America, by Isaac 
Lea, Esq. of Philadelphia. 
Genus LII. —SCALARIA. — Lamarck. 
Generic Character. Shell turreted, oblong or ovate ; body 
short ; spire long, composed of gibbous, distinctly defined 
volutions, which are, in some species separated ; with longi- 
tudinal, elevated, subacute, interrupted, oblique ribs, in some 
instances so thickened as to assume a varicose appearance; 
aperture almost orbicular, but mostly a slight degree longer 
than broad, with a thickened reflected margin ; lower part 
of the columella, formed into a subcanaliculate shape; outer 
lip continuous, entire ; operculum horny, thin and spiral. 
Scalaria tenuelamella, Plate V. fig. 20. Found in the 
Chalk of the Paris basin. 
In one or two species the ribs are indistinct, being hardly elevated above the 
volutions; and the reflected margin of the outer lip is most apparent in those 
species, in which the volutions do not touch each other. 
This genus contains but few species, and these inhabit the ocean. Fossil 
species occur in the Calcaire-grossiér of Grignon, the newer formations of 
Italy, the Crag of England, and London Clay. 
Genus LIII. — RISSOA, — Freminville. 
Generic Character. — Shell oblong or turreted, and much 
acuminated ; body short, spire long, consisting of numerous 
volutions, aperture entire, oval, oblique, dilated, rather 
angulated above, with a slight sinus at the base of the colu- 
mella ; lips nearly united ; outer lip slightly thickened, but 
its edge not reflected ; operculum horny. . 
Rissoa acuta, Plate LV. fig. 16, Found in the great 
Oolite at Ancliffe. 
The outer lip being more thickened than the ribs, but not producing varicose 
sutures, together with the obscure sinus, or truncation at the base, are well- 
marked characters of this genus. The species are all small, inhabiting the 
ocean ; and are pretty numerous in the Mediterranean. 
Fossil species are only found in the great Oolite, and newer strata of the 
Tertiary formations. 
Genus LIV.— EUOMPHALUS. — Sowerby. 
Generic Character. — Orbicular, conical, spire short, con- 
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