CONCIUFERA. 
449 
teeth in each valve, two of which are approximate and the other 
remote ; with the ligament subexternal; umbones turned much 
to one side; beneath which is an elongated cordiform depression ; 
cartilage slope much depressed, with an elongated groove in the 
right valve for the reception of the margin of the left valve. 
Ortygia gallina. — The Hen Ortygia. 
Plate LXXXIX. fig. 19. 
Somewhat heart-shaped with obtuse recurved concentric striae, 
and three or four radiated bands proceeding from the umbo to 
the margin, frequently with zigzag markings throughout; inside 
white, the margin finely crenated. One inch long. Inhabits 
the British seas. 
Genus 21. —VENU S. —Linnet us. 
Generic Character. —Equivalve, inequilateral, transverse, or 
suborbicular; hinge with three teeth in both valves, all approxi¬ 
mate, the lateral ones divergent at their summits; ligament ex¬ 
ternal ; having cordiform depressions beneath the beaks. 
Venus Casina. — The Monticassina Venus. 
Plate LXXXIX. fig. IS. 
Suborbicular, with transversely acute recurved ridges, crenu- 
lated on the hind margin ; slightly channelled behind the de¬ 
pression. Two inches long. Inhabits the British seas. 
Genus 22. — CYTHEREA.— Lamarck. 
Generic Character. —Equivalve, inequilateral, suborbicular, 
trigonal, and transverse ; right valve with four primary teeth, of 
which three are divergent and approximate at their base, and one 
remote; three primary divergent teeth in the opposite valve, and 
a hollow; margin parallel; without lateral teeth. 
Cytlierea Chione. — The Chione Cytherea. 
Plate LXXXIX. fig. 21. 
Somewhat heart-shaped, strong; covered with a chestnut 
glossy epidermis, faintly wrinkled transversely, longitudinally 
rayed; with a cordiform depression under the beak. Two and 
a half inches long. Inhabits the British and Mediterranean 
seas. 
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