DIMYARIA. 155 



GenusU.— SAXIC AY A.^ Lamarck. 



Generic Character. — Inequilateral, obtuse, and transverse ; 

 the anterior upper margin gaping ; hinge nearly without teeth ; 

 ligament external. 



Saxicavaprcecisa — The Abbreviated Saxicava. Plate 

 XVII. fig. 18. Oblong, wrinkled, one valve larger than the 

 other, truncated at the posterior end; of a pale horn colour. 

 Three quarters of an inch broad. Inhabits the British seas, 

 in cavities bored in rocks, stones, and wood. 

 It is probably only a variety of Saxicava rugosa. 



TRIBE III. CORBULACEA. 



Inequivalve shells, with an internal ligament ; one of the 

 beaks always proiecting beyond the other. 



Genus 45. — PANDORA. — Lamarck. 



Generic Character. — Shell regular, inequivalve, inequi- 

 lateral, transversely oblong; upper valve flattened, lower 

 convex; hinge with two oblong, diverging cardinal teeth, 

 in the upper valve, and the other valve with two oblong 

 grooves ; ligament external. 



The hinge some-.vhat like that of Placuna, but more nearly allied to 

 Corbula, having two muscular impressions. 



Pandora rostrata. — The Beaked Pandora. Plate 

 XVII, fig. 19. White, oblong, much produced towards the 

 beak ; one valve nearly flat, the other convex ; rounded at 

 the anterior end. One inch broad, lidiabits the Mediter- 

 ranean and British seas. 



Genus AQ. — CORBULA Bruguiere. 



Generic Character. — Shell regidar, inequivalve, inequi- 

 lateral, closed or slightly gaping ; with a conical, bent, 

 ascending, primary tooth in each valve; a small pit at its 

 side ; destitute of lateral teeth ; ligament external. 



