66 CLASS REPTILIA. 



all that I ever saw, the most concave ; a foot long, eight 

 inches over, and almost six inches high. The convex is 

 curiously wrought with black and whitish pieces, alternately 

 wedged in one against the other, and notched, as it were, 

 with transverse incisions. Those near the margin and on the 

 sides are composed into several pyramidal areas, or great 

 triangles, whose bases are about two inches broad ; on the 

 back, into six angular ones, each of them convex ; on the 

 sides, and quite behind, the shell is carried somewhat inward ; 

 before and hinderly, the edges are toothed, and bended out- 

 ward and upward. The inward edges are covered with 

 shelly plates above an inch and a half broad. The concave 

 is composed of six and forty bones. Along the middle of the 

 back are twelve, all, except the foremost and the four last, 

 almost square. Next to these are eight on each side, like so 

 many contiguous ribs, together with two lesser square bones 

 before. Next to these, eight more, as it were, under-ribs on 

 each side. To the twelve middlemost bones, the ribs are 

 joined by an alternate commissure, so that one of them 

 answers to the halves of two ribs, and vice versa. To these 

 the under ribs are attached in a wonderful manner, viz. by 

 a branched suture or indenture. For the great teeth of the 

 under ribs being first inserted into those of the upper ribs, 

 the indenture is afterwards repeated by lesser teeth, out of 

 the sides of the great ones. Besides the most elegant order- 

 ing of the work, in the convex there are three things chiefly 

 observable, which serve for the greater strength of the shell. 

 That is to say, the convexity of the several areas on the back, 

 the branched sutures, and the alternate commissures of the 

 bones ; answerable to the rule of nature in a human skull, 

 and of art in laying of stones in buildings, and in covering of 

 broader vaults, not with one arch, but several lesser ones, for 

 the greater strength." 



Dr. Shaw seems to consider that this tortoise is also a 



