126 DIMYAIRA. 



TRIBE V. CONCHACEA. 



With at least three primary teeth in one valve, and the other 

 generally the same, although sometimes vi^ith less. 



Sub-division I. — Inhabiting the sea. Usually destitute of 

 lateral teeth. 



Genus 19 — VENERICARDIA Lamarck. 



Generic Character — Equi valve, inequilateral, suborbicular ; 

 the sides generally with longitudinal radiated ribs ; hinge with 

 two oblique teeth in each valve, turned in the same direction. 



Venericardia imbricuta. — The Imbricated Venericardia. 

 Plate XVI. fig. 17. Suborbicular, having convex longitudinal 

 ribs, covered with imbricated, rough scales. One and a half 

 inch long. Fossil at Grignon. 



Germs 20.— ORTYGIA — Leach. 



Generic Character. — Shell equi valve, transverse, three primary 

 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 XVI. fig. 19. 

 Somewhat heart-shaped with obtuse recurved concentric stria?, 

 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— VENUS— Lmn^M.f. 



Generic Character.— EqmvaUe, inequilateral, transverse, or 

 suborbicular ; hinge with three teeth in both valves, all approxi- 

 mate, the lateral ones divergent at their summits ; ligament ex- 

 ternal J having cordiform depressions beneath the beaks. 



