248 ARCADiE. 



one to which the beaks incline. The extremity of this, 

 although nearly equally broad with the other, is more or 

 less subangulated at, or a little above, the middle ; the 

 opposite end is broadly rounded, the declination, how- 

 ever, not vying with the basal ascent. The projecting 

 umbones (which are occasionally oblique) are central, or 

 nearly so ; the ligamental area is moderately long, and 

 rather narrow. The interior is either white or brownish 

 chocolate colour ; if the former, then, for the most part, 

 with more or less extensive stains of the darker hue upon 

 the subangulated side ; if the latter, with the muscular 

 impression upon the rounded side almost always free from 

 colouring matter. The former painting prevails chiefly in 

 glycimeris, where the central portion of the hinge-margin 

 is narrow ; the latter in pilosus, where that part is generally 

 dilated at the expense of the ligament. 



The number of teeth is very variable, extending at fewest 

 from six to twelve on each side ; as a general rule they are 

 least numerous in those shells with a white interior, and 

 are always more plentiful on the subangulated side. A 

 kind of velvety epidermis, of a yellowish-brown colour, 

 varying much as to closeness or looseness of texture, 

 clothes, for the most part, the exterior of the valves in the 

 vicinity of the margin. 



Two inches may be regarded as the full diameter of the 

 ordinary run of British examples ; occasionally shells are 

 taken of half an inch more in measurement, but the mass 

 of individuals are ordinarily half an inch less than what 

 we have stated. Our native specimens of the variety 

 pilosus are inferior to the other in size ; exotic ones, on 

 the contrary, surpass it in that particular. 



The animal is shaped like the shell ; its mantle is freely 

 open, except in the region of the hinge ; the margins are 



