THE EURYPTERIDA OF NEW YORK 45 
icerae serve to suggest the ready reversibility of the pincers. On com- 
paring the length of the pincers with that of the arm [specimen pl. 77, fig. 
3] one finds that the pincers are as long as the uncontracted part of the 
arm. The contracted basal portion, which amounts to about one fifth 
of the length of the arm is, as our material and the drawings of the British 
specimens indicate, nearly always missing. In another specimen, 
this part contrasts by its thinness with the thicker test of the arm, 
which terminates abruptly at a convex line along the contracted part. 
One might at first glance infer the presence of an articulation at 
this point, but the continuance of the test and the contrast in thickness of 
‘it on the arm and of the basal contracted part show that this latter was 
rather of the nature of a membrane and probably a part of the epistoma, 
Its basal edge is ragged and obviously torn. 
The corresponding lengths of the pincers and arms and the actual 
occurrence of pincers thrown: back, demonstrate, we believe, the functional 
possibility and competency of the pincers to grasp food and carry it to the 
mouth. The crustaceans afford several instructive examples of analogous 
prehensile organs. One of these is the giant spider crab from Japan (Mac- 
rochirus kampferi) seen now in many of the larger museums. 
It possesses a pair of immensely long prehensile chelate limbs which con- 
sist of two long segments and the chelae, besides a small proximal seg- 
ment. In the articulation it can be doubled in the exact middle between 
the two equally long segments, thus serving to bring the prey readily 
within reach of the masticating edges of the other limbs surrounding the 
mouth. 
In the restorations of Pterygotus, a varying number of segments 
has been assigned to the chelicerae. Salter and Huxley [op. czt. pl. 15, fig. 6] 
gave four segments (the supposed additional basal ones not visible in the 
dorsal view), but Woodward doubled this number in his figure [op. czt. pl. 8, 
fig. 1]; and the latter is retained by Schmidt [op. czt. p. 73, fig. 1B] and has 
long since entered the textbooks. While Salter and Huxley figure the 
chelicerae as rigidly straight, as they are indeed seen in our specimens, 
