The Fossil Crab of Gay Head. 585 



1.5. It is much curved, in a longitudinal sense, so that 

 the suj)erior outline in a side view forms the arc of a circle, 

 the middle height of which would be nearly half an inch. 

 It must be here stated that the diagram, (Plate XII., fig. 

 Ij) represents the crab turned up into such a position as 

 best to show the anterior portion, while the posterior portion 

 is foreshortened. In a transverse sense, the carapax is but 

 slightly convex anteriorly ; posteriorly the median or greater 

 part is nearly flat, but there is on either side a well-defmed 

 longitudinal channel or concave depression, where the 

 branchial region slopes abruptly toward the postero-lateral 

 margin. The surface is smooth and covered with minute 

 punctures, except anteriorly and at the margins, where 

 it becomes distinctly granulated. The central region 

 is defined by two lunate marks, which, though not pro- 

 jecting above the general surface, are conspicuous by their 

 smoothness and darker color, and serve as a sign by 

 which some fragments of the carapax of this crab may al- 

 ways be recognized. 



The antero-lateral margin is armed with four teeth, the 

 first or anterior one forming the outer angle of the orbit. 

 The second and fourth teeth are about equal, and scarcely 

 more distant from each other than the first and second, 

 while the third is very small, as if supplementary and in- 

 tercalated between its neighbors. The orbits are elongated, 

 each occupying nearly one third the width of the carapax, 

 and have an entire, though granulated superior margin. 

 As far as can be discovered in the specimens at hand, there 

 is no notch between the front and the orbit, at the attach- 

 ment of the external antenn;e, for the inner angle of the orbit 

 forms, apparently, the outer angle of the front. The front 

 occupies about one fourth the breadth of the facial region, 

 and has a small projecting lobe at the middle, which is 

 divided in two by a median emargination. 



The chelipeds are of moderate size, and resemble in gen- 



JOUKNAL B. S. N. IF. 74 



