72 SAXICAVID^E. 



Serpula triquetra at Guernsey, Lulworth, and other 

 places. Coralline Crag (coll. S. Wood). Its extra- 

 British localities are the Boulonnais (Bouchard-Chan- 

 tereaux) ; Croisic in lower Brittany (Cailliaud) ; coast 

 of Spain (M f Andrew) ; Gulf of Lyons (Martin) ; 

 Cannes (Mace) ; Spezzia (J. G. J.) ; and Tunis, in 25 f. 

 (M f Andrew). 



M. Binghami does not appear to have the power of 

 excavating stones or shells, because specimens thus en- 

 closed are frequently distorted or constricted, so as to 

 fit the holes which they occupy. Its habits in this 

 respect are the same as those of Tapes pullastra var. 

 perforans, Thracia distort a, and some other bivalves. 

 My largest specimen is scarcely three-quarters of an 

 inch in breadth ; but the late Dr. Lukis obtained much 

 larger ones from the cavities left by Saxicavce at 

 Guernsey. It differs from M. truncata of the same 

 size in being more inequivalve, inequilateral, and com- 

 pressed; in the anterior side being invariably and ab- 

 ruptly truncated, instead of rounded ; in the posterior 

 extremity being more straight, and having a smaller 

 gape; in that side being distinctly angulated, espe- 

 cially in the left valve ; and the tooth in the left valve 

 is less raised. It, however, belongs unquestionably to 

 the same genus. 



Family XXI. SAXICA'VID^, Swainson. 



BODY oval or oblong: mantle thick: tubes more or less 

 united ; orifices fringed with cirri : gills unequal on each side : 

 palps triangular : foot finger-shaped, occasionally byssiferous. 



SHELL rhomboidal, more or less inequilateral, and in the 

 genus Saxicava sometimes inequivalve, always gaping at the 

 posterior end (where it is obliquely truncated), and sometimes 



