( 11 ) 



12. Venus. Lin. M. 



Equivalved, inequila- 3 cardinal teeth close Ligament exterior, co- 

 teral, suborbicular. Fig. together on each valve, vering the furrow. (1) 

 29 and 30. lateral teeth diverging 



at the summit. 



a. Internal edge of valves crenated or den- ( Striae scaly. 



tated. I Striae not scaly. 



b. Internal edge of valves entire. 



Equivalved, inequilate- 

 ral, sub-orbicular, with 

 longitudinal radiating ribs. 

 Fig. 32. 



2 oblique cardinal 

 teeth, directed to the 

 same side. 



43. Yenericardia. Lam. 

 M. Foss. 



44. Crassina. Lam. M. 

 Astarte. Sowerby. 



Sub-orbicular, equival- 

 ved, sub - inequilateral, 

 close. Fig 34, 35. 



45. Cyprina. Lam. M. 



Equivalved, inequilate- 

 ral, like an oblique heart ; 

 beaks obliquely curved. 

 Fig. 33. 



Hinge with 2 strong 

 diverging teeth on the 

 right valve, and 2 very 

 unequal on the other 

 valve. 



3 unequal cardinal 

 teeth, close together at 

 their base, a little di- 

 verging at the top : i 

 lateral tooth, distant 

 from the hinge, on the 

 anterior side, some- 

 times obscure. 



Ligament exterior. (2) 



Ligament exterior, on 

 the longest side ; gene- 

 rally a third muscular 

 impression, very small. 

 (3) 



Ligament exterior, 

 partly sunk under ths 

 beaks : callosities of the 

 inner edge large, arched, 

 terminated near the 

 beaks by a hollow. (4) 



fl) There are a few species which have their teeth almost straight; they gene- 

 rally live in the sand at a moderate distance from the water's edge ; they are more 

 numerous and varied in warm climates. Foss. in Crag Marl, Green Sand, London 

 Clay ; at Grignon, Pontcharlain. 



(2) Foss. in the London Clay, at Grignon, Beauvais, Couriagnon, Cambray, I'Oise, 

 Essanville, Italy, Piedmont, Angers, Paris, Marl pits of Touraine, Chaumont. 



(3) Foss. Crag Mart, Portland-rock, Oak-tree Clay, Under Oolile. 



(4) By their lateral tooth (sometimes obscure) and their persisting epidermis, 

 the Cyprinm approach the fluviatic Concha, and it is probable that many live in the 

 sea, at the mouths of rivers. Foss. at Sienna, Turin, Italy, Bourdeaux, England, 

 Piedmont. 



