PALEONTOLOGY OF NEW YORK. 



sub-triangular in outline, with their apices posterior, very convex on their 



anterior surface and elevated along their longest axis. The masticating 



ue parallel, approximate, moderately broad and bear four or five 



lenticles of which the posterior is apical. Their substance is tenuous as in 



rapace, excepl upon the crown, where it is sufficiently thick to retain 



Mini without distortion. A very large carapace, 90 mm. in length, 



which belonged to the largesl individual yet observed, shows a single 



mandible somewhat out of place, and compressed in such a manner as to 



i the masticating edge. It shows, however, a long process at the 



anterior extremity (" manubrium," Beecher), which has been broken off at 



up. Such a process is often noticed in detached mandibles, to which 



reference will presently be made, but of the two specimens referred to in 



which these organs are undisturbed in the rock, the mandibles of the 



iller evidently lacked any such processes, and those of the latter are 



erved as not to show them had they existed. These mandibles are 



situated within the posterior hall' of the carapace, and are at least one-third 



thi cat i pace itself. 



>HBN long, slowly tapering to the caudal plate, and composed of six somites, 



which increase in length posteriorly, the ultimate joint being as long as the 



lirst two, and one-half longer than the penultimate. The anterior and pos- 



targins of each somite are slightly elevated and incurved on both 



dorsal and ventral sides; the dorsal surface is rounded and gently concave 



. excepl upon the last somite. The posterior margin of each somite 



short incurved spines, in three pairs. The strongest pair of these 



ll "' d orsa ] surfaci cond and somewhat shorter pair upon the 



surface, and a third [.air (in young individuals often very 



upon th- lateral margins. Upon the anterior somites these spines are 



quite Bmall or visible only as nodes. The ventral surface bears 



'ticulating surfaces of the somites are broad, and when 



men is normally extended they come into actual contact only at 



both the dorsal and ventral margins distant, a fact which 



" I >>. Beecher) greal freedom of motion in these parts. 



