308 
PALAEONTOLOGY OF NEW-YORK. 
The first joints of this last pair of feet are broad subrhomboidal plates, already 
noticed as covering the posterior half of the carapace, the adjacent edges of which 
are serrate for the purposes of manducation. The second joint is short and stout, 
and articulated to the first one by a strong process. The third joint is very short. 
The fourth joint is usually equal to, or longer than the two first. The fifth and 
sixth joints are smaller. The seventh joint is suddenly dilated, wider and longer 
than the preceding, rliomboidal, having the penultimate joint articulated close to 
its distal anterior margin; while along two-thirds of its Avidth there is a tri¬ 
angular piece attached by a soldered suture*, the sloping edge of which forms 
one side of the pincer-like chela. The eighth joint is subovate, rarely narrower 
at its upper extremity, and articulated nearer to its anterior edge; so that in- its 
motions, it had the inner cutting edge placed against the sloping side of the tri¬ 
angular process of the preceding joint : thus the inner adjacent edges of these 
parts Avere fitted to move over each other as the blades of a shears, one being 
relatively fixed and the .other free. The extremity of the last joint is bilobed at 
the tip for the articulation of a terminal palette, as shoAvn in the figure. 
In the articulation of the joints of these appendages, there is much more 
freedom at the base of the seventh joint, which, Avith the succeeding one, forms 
a prehensile chelate extremity of peculiar character. 
The post-oral plate appears to be attached simply by the muscles to the parts 
beloAV. 
The first or double segment of the body on the loAver side, Avith its appendages, 
sometimes occurs separated from other portions of the body; as in the accompanying 
figure, which is copied from one of these separated joints. 
Fig. 3. 
The anchylosed first and second segments 
of the body, 1 A 2. The suture ss marks 
the line which, on the back, is the articu¬ 
lating line of the two segments. 
The parts a a are two intercalated pieces 
joined by sutures to the other parts, the 
outer suture lines not reaching to the upper 
edge of the segment. 
b, the first joint of the locomotive ap¬ 
pendage. 
c, the second joint of the same. 
, the extreme free appendages of this organ. 
In the centre of the upper division of this joint are inserted two pieces, leaving 
a triangular space or emargination behind, into which the locomotive appendage is 
inserted and joined by sutures : although dividing the lower half of the articula- 
* I infer this to be a suture from the fact that there is always a visible dark line along the junction, and 
an apparent slight thickening of the substance left in the stone, while the parts are not unfrequently sepa¬ 
rated along this line. 
