178 ARCID.E. 



times distinctly visible in front: beaks small, not very pro- 

 minent, blunt and slightly recurved : ligament thin, and re- 

 sembling that of A. pectuncidoides in every respect, except 

 that in the present species it is of a lozenge shape, corre- 

 sponding with that of the ligamental cavity, which is deep ; 

 the number of cords is between 40 and 50 : hinge-line quite 

 straight, and forming an obtuse angle at each end, occupying 

 about two-thirds of the entire breadth of the shell: hinge- 

 plate as in the last species : teeth about 35, small and straight 

 in the centre of the hinge, becoming larger and diverging 

 obliquely and gradually towards each side, so as to form a 

 gently curved row ; each tooth is fiuely striate on both sides : 

 inside porcellanous, marked lengthwise with remote striae to 

 within a short distance from the margin, which is usually 

 quite smooth and plain, although occasionally the left valve is 

 slightly crenulated, especially on the posterior side : pallial 

 scar entire : muscular scars very large and well defined, of a 

 quadrangular shape. L. 0-45. B. 0*65. 



Habitat : Gravel, from 15 to 25 fathoms, on the 

 English, Welsh, and Irish coasts, from Berwick Bay to 

 Jersey, and also at Oban (Bedford), where it becomes 

 rare. It is fossil in the Bed and Coralline Crag, as 

 well as in the Subapennine and Sicilian tertiaries. 

 M"' Andrew has taken it at low water in Algarve, and 

 Forbes at from 10 to 150 fathoms in the iEgean ; it is 

 common in the Mediterranean, and ranges to the Canary 

 Isles ; bnt it does not appear to have been found north 

 of the British Isles. 



Lister first noticed this species as English ; and 

 Dr. Pulteney called it the " hairy ark-shell." Mr. Clark 

 has remarked that the foot is very like that of Galeomma 

 Turtoni, showing the connexion between the latter and 

 the present genns, in respect both of the animal and 

 the shell. A. lactea is usually fixed by its byssus to the 

 inside of old bivalve shells, or (in the south of Devon) 

 wedged in crevices of loose fragments of New Red sand- 

 stone. The latter circumstance induced Turton at one 



