136 DIMYAIRA. 



Nearly allied to the Venus, but the teeth are differently disposed, having 

 three primary teeth in one of the valves, at least. 



Venerupis perforans. — The Perforating Venerupis. Plate 

 XVII. fig. 16. Sub-rhombic, transversely striated, wrinkled 

 on the anterior side; brown, with a white inside, sometimes 

 with a tinge of purple. Three quarters of an inch broad. In- 

 habits the British seas, boring into rocks and clay. 



Genus 43 TETRICOL A.— Lamarck. 



Generic Character. — Subtrigonal, transverse, inequilateral; 

 posterior side rounded, and the anterior attenuated, and slightly 

 gaping ; hinge with two teeth in each valve, or in one valve 

 only. 



Petricola pholadiformis.— The Phol as- Shaped Petricola. 

 Plate XVII. fig. 17. Transversely elongated ; umbones very 

 small ; with transverse, rough, prickly striae ; posterior side ex- 

 tremely short. Three inches long. Inhabits the Australian 

 seas, boring into wood and rocks. 



Genus U.— SAXIC AY A.— LamarcL 



Generic Character. —Inequilateral, obtuse, and transverse ; the 

 anterior upper margin gaping ; hinge nearly without teeth ; 

 ligament external. 



Saxicava pracisa. — 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. 



TRIBE III. CORBULACEA. 



Inequivalve shells, with an interior ligament ; one of the 

 beaks always projecting beyond the other. 



Genus 45. — PANDORA Lamarck. 



Generic Character. — Shell regular, inequivalve, inequilateral, 



