142 ARCID.E. 



are crossed by finer longitudinal striae or ribs, giving the sur- 

 face a cancellated appearance ; these markings are coarser and 

 more irregular at the sides, but they do not extend to the 

 lunule or space below the beaks : colour flake- white under the 

 epidermis, which is thickish, olive-green, and microscopically 

 striate like hair-cloth in a transverse direction : margins an- 

 gular and slightly truncate on the anterior side, curved in 

 front, and expanding on the posterior side to a wedge-shaped 

 but rounded angle : beaks rather prominent and blunt, slightly 

 recurved : hmule furrowed obliquely by strong and irregular 

 wrinkles (being a continuation of the transverse striae), and 

 indented or grooved in the direction of the beaks ; it is sepa- 

 rated from the rest of the shell by a ledge, and projects in the 

 middle so as to form a distinct keel : ligament narrow but 

 strong : cartilage small, pear-shaped, contained in a narrow 

 cavity underneath the beaks and projecting inwards : hinge- 

 line gently curved : hinge-plate broad and strong, occupying 

 the whole of the dorsal space and rather more than one-third 

 of the circumference of the shell : teeth sharply pointed, 10-12 

 on the anterior side and 20-24 on the posterior side of the 

 cartilage-pit, arranged in nearly straight rows, which diverge 

 outwards at almost a right angle; they become larger as they 

 recede from the beak, in consequence of the progress of 

 growth : inside cream-colour and slightly iridescent, faintly 

 striated, or marked with lines which radiate from the beak and 

 terminate in distinct notches or crenulations on the anterior 

 angle and in front ; but these notches do not extend to the 

 posterior angle : muscular scars oval and conspicuous. L. 0-65. 

 B. 07. 



Habitat : Sandy mud and clay on the west coast of 

 Scotland, at various depths, as well as in Dublin Bay 

 (Branscombe and Warren) ; Bantry Bay (Humphreys) ; 

 and south-west coast of Ireland (M f Andrew). Captain 

 Bedford has dredged it in a semifossil state at Lismore, 

 imbedded in a concrete of indurated clay. It is a local 

 species. Loven, Asbjornsen, and Malm have recorded 

 it from several parts of the Scandinavian coasts, the 

 second of these authors giving 15-20, and the last 14-35 

 fathoms. It also inhabits the coasts of Spain and both 

 sides of the Mediterranean, as well as the iEgean, where 



