CYPRINA. DIMYARIA. 101 
Section 3. External surface smooth and covered by a thin velvety epider- 
mis; four or five divergent cardinal teeth; an elongated, nearly lamellar an- 
terior lateral tooth ; muscular impression of the mantle with a large rounded 
sinus; lunule elongated and indistinct ; beaks less inclined forwards than in 
the preceding section. [Illustrated by C. corbis. 
Section 4. External form nearly oval, anterior side much shorter than the 
posterior; outside smooth, and covered by a thin corneous epidermis; a few, 
however, are grooved longitudinally; three divergent cardinal teeth in each 
valve, and a closely approximated, blunted lateral tooth; pallial impression 
very large, and usually pointed at its anterior end. C. Erycina, and Chione, 
are examples of this group. 
~ We have removed those shells of a lenticular form, such as C. exoleta, and 
its congeners, and constituted a new genus with them, under the title of 
Artemis. * This genus was instituted by Poli. 
The Cytheree inhabit the ocean ; and are distinguished from the Veneres, 
and the. Cyprinz, by having a lateral tooth; and from the Lucinz, by the 
form of the muscular impression. 
Fossil shells of this genus are principally met with in the Tertiary forma- 
tions, the London Clay, Calcaire-grossier, and Greensand ; and several species 
occur in the Oolitic group of rock. 
Genus XX VII. — ARTEMIS. — Poli. 
Generic Character. — Shell nearly lenticular, externally 
and concentrically grooved; beaks much turned to one 
side, beneath which is a short, strongly-marked cordiform 
depression ; three cardinal teeth in each valve, two of which 
are contiguous, and the other divergent, which is broad in 
the right valve, cleft in the centre, to receive that of the 
opposite valve, which is slender, with a small lateral and 
closely approximated tooth; pallial impression with a large 
oblique and straight-sided sinus; cartilage external. 
Artemis lentiformis. Plate X. fig. 16. 
The shells of this genus are marine, and live in deep water. Fossil species 
are rare, and occur in the Crag of Essex and Sussex. 
Genus XXVIII.— CYPRINA. — Lamarck. 
Generie Character. — Shell ventricose, equivalve, inequi- 
lateral, suborbicular, obliquely heart-shaped ; umbones 
obliquely curved, anteriorly ; three cardinal teeth in each 
valve, approximated at their bases, and divergent above, 
with a posterior lateral tooth remote from the primary teeth ; 
external surface covered by a thick, rough, dark, horny 
epidermis ; each valve with two lateral, remote, muscular 
impressions ; pallial impression with a slight sinus ; ligament 
* Genus Exourra, of our “ Illustrations of the Conehology of Great Britain and 
Ireland,” first edition, and of our “ Conchologist’s Text Book,” 
