AURICULA. TRACHELIPODA. 61 
adult state ; peritreme, or outer lip, more or less angular at 
the upper parts united all round, sometimes thickened, 
usually reflected, and frequently externally fringed ; oper- 
culum spiral, generally horny, but inclining to testaceous in 
some species ; consisting of a few depressed convolutions, 
provided with a simple testaceous internal coating. 
Cyclostoma antiqua. Plate IV. fig. 5.* 
Several of the species approach nearly in form to the Paludine and 
Valvate, but the orbicular aperture, and entire outer lip at ouce distinguish 
the Cyclostomata from the shells of these genera, independently of their being 
fiuviatile. 
The Cyclostomata are all land shells, and the species very numerous, 
amounting to about ninety. They chiefly inhabit India, the West Indies, 
and South Sea Islands ; a few are natives of Europe, and three are found in 
Britain. 
Various species are known in a fossil state, and these are only met with at 
Grignon, in the Calcaire-grossier, 
Genus LXXIX.— NEMATURA. — Benson. 
Generic Character. — Shell thin, almost oval, a little 
compressed from back to front ; body large, contracted near 
the aperture ; spire small, consisting of few inflated volutions 
terminating in an acute apex; aperture small, oblique, 
rounded below, and a little contracted above; outer lip 
continuous, and thin ; operculum horny, spiral, with few 
convolutions, 
Nematura Delte. Plate VI. fig. 20. 
A distinguishing character of the shells of this genus is the contraction of the 
body volutions near the aperture. They are all very minute. 
The Nemature are marine shells, and but two recent species are known. 
One fossil species only has been discovered. 
Genus LXXX. — AURICULA. — Lamarck. 
Generic Character, — Shell solid, oval, or oblong-ovate, 
cylindrical, or conic ; body large, spire very small, obtuse ; 
aperture elongated, narrow, generally contracted near the 
centre, and rounded below; inner lip with two or three 
strong plaits ; outer lip thickened, reflected or denticulated; 
covered with a horny epidermis. 
Auricula ventricosa. Plate IV. fig. 31. Found in the 
Crag at Ipswich. 
Section 1.— Shells conical, with two or more folds on 
the inner lip; .aperture narrow, outer lip thickened. 
Example A, ventricosa. 
Seciion 2. — Shells somewhat round ; only one fold on 
