132 FISTULANA. 



of sp. 1, but much narrower. Tlie tubes in course of 

 growth agglutinate the sand particles and minute pebbles 

 surrounding them in their burrows. 



3. GRANDis, f. 16, Deshayes. — Valvse latse postice rotunde 

 ventricosse. Tuba concentrice annulata. — At the posterior 

 end the valves are broad and curiously swollen outside, with 

 a corresponding hollow inside. 



Genus SAXICAVA. 

 Plate 471, f. 1-14. 



Molluscum perforans. Testa oblonga, sequivalvis, ingequi- 

 lateralis, ad marginem ventralem hians ; epidermide tenui 

 induta; cardine setate juniori acute bidentato, setate majori 

 edentulo ; ligamento externo, super fulcrum affixo, impres- 

 sione pallii postice late sinuate. — The rock-boring Mollusca of 

 this genus have oblong, equivalve inequilateral shells, which 

 when young have minute cardinal teeth. These disappear 

 afterwards. There is an hiatus in the ventral margin for 

 the passage of a byssus. 



Species. 



1. ARCTiCA, f. 1, Linnceus. — Eecta, rugosa, elongato- 

 subquadrata, postice biangulata; (setate juniori ad angulum 

 spinosa) ad terminum late truncato. — Not constant in shape, 

 but inclined to be straight, angular, and broadly truncated. 

 The young shells are narrow and rounded in front, ventricose 

 at the posterior ventral margin, and spinose on the posterior 

 angle. 



2. AUSTRALis, f. 2, Lamarck. — Tortua, rugosa ; umbonibus 

 magnis, elevatis, fere terminalibus ; margine dorsali arcuato, 



