26 CONCHYLIA— DJTi/yi?^. 6. 



Shell transverse, equivalve, inequilateral, open at the anterior end. 

 Hinge with two teeth in one valve closing between three in the 

 other : lateral teeth none. Ligament external. 



The individuals of this family, like most of the inhabitants of 

 rocks, are exceedingly variable in their figure and outline. In tho 

 structure of the teeth they much resemble the genus Venus ; but 

 we believe that there are uniformly only two in one of the valves, 

 with sometimes the obscure rudiment of a third, and three in the 

 other : the gape also, or opening at the anterior end, materially dis- 

 tinguishes them. With the Donax tribe they have no relative con- 

 nexion. They are imbedded in rocks, or found wedged in the 

 interstices. 



IlKS, 

 1. 



Petricola testa polymorphd, lamellis transversis reflexw, inter stitfts 



longitudinaliter striatis. 

 Shell variously shaped, with transverse reflected plates, the inter- 

 stices of which are striate longitudinally. 

 Tab. nost. 2, fig. 14. 

 Donax Irus. Linn. Syst. Nat, p. 1128. 



Gmelin, Syst. p. 3265. 



Turton, Linn. Syst. iv. p. 216. 



Pennant, Brit. Zool. iv. p. 200. 



Chemnitz, vi. p. 571, tab. 26, fig. 268 to 270. 



Montagu, Test. Brit. p. 108 and 573. 



Donovan, Brit. Shells, i. tab. 29, fig. 2. 



Linn. Trans, viii. p. 77. 



Turton, British Fauna, p. 156. 



Dorset Catal. p. 34, tab. 12, fig. 6, left hand. 



