AST ARTE. 453 



The union of A. Scotica with A. Danmoniensis may 

 excite some little surprise and hesitation among naturalists, 

 and, indeed, was only acceded to by ourselves after a 

 protracted scrutiny, and the examination of some hundreds 

 of specimens assembled from the widest range of localities. 

 In no respect did individuals of the former differ from 

 those of the latter variety, excepting in the crenulation of 

 the margin, and as specific differs from varietal diversity 

 mainly by the greater number of permanent distinctive 

 characteristics, we cannot separate into two species shells 

 only unlike in the presence or absence of a single feature. 

 With regard to the greater or lesser approximation of the 

 ribs, and their consequent proportion to the interstices, no 

 stress can be laid upon this point, as the more rapid is the 

 growth of the animal, the more remote do these become ; 

 thus, in the southern Astartes, which are more speedily 

 developed, the ribs are more distant, whilst in the more 

 northern examples, whose progress to maturity is more 

 sluggish, and whose growth is not unfrequently stunted, they 

 are sharper defined, and more closely arranged. 



Like most of the Astartes, its contour is very variable ; 

 it is, however, longer than broad, and more or less sub- 

 triangularly heart-shaped ; some northern individuals, how- 

 ever, are so abbreviated in shape that their breadth nearly 

 (but not quite) equals their length, and their form con- 

 sequently becomes suborbicularly trigonal. The valves 

 are always solid and opaque, more or less convex, at times 

 even ventricose, and are covered with an unpolished cuticle 

 or thick adherent epidermis, which varies in colouring 

 from bright yellow to rufous chestnut ; beneath this the 

 surface is whitish, or pale rufous, and concentrically 

 lyrated with from abovit twenty to thirty more or less 

 elevated ribs, which are almost always, if not invariably. 



