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1883. ] 23% [Claypole, 
anchor-shank with its two arms. Right and left of the anterior tuber- 
cle, and not quite half way between them and the margin, arise two 
broad, rounded prominences anteriorly, elongated and connected with the 
median ridge by a scarcely perceptible elevated tract. 
The whole surface of the head is covered with small wrinkles or tuber- 
cles, the former chiefly in front, the latter behind, and the margin is 
marked by a narrow groove about one-eighth of an inch in breadth, resem- 
bling that which often marks the head of a trilobite. 
No trace of bone can be found upon the specimen, so that there is no 
ground for supposing that it is the head ofa fish. But the greater part of 
the surface is covered with a thin, black, perhaps carbonaceous, coating, 
highly suggestive of the carapace ofa crustacean, This is, beyond doubt, 
its nature, and the fossil represents a large species hitherto unknown, and 
from an horizon which has thus far yielded nothing similar to it. The 
only crustaceans yet announced from the Catskill are some small entomos- 
tracans mentioned by the writer at the meeting of the American Associa- 
tion at Montreal. The specimen in question possesses therefore an un- 
usual interest. 
From so small a portion of the specimen it is difficult to assign it its ex- 
act place in the animal scale, but among the crustaceans we are led im- 
mediately to look at the allies of the existing king-crab, Limulus, and 
those of the fossil Hurypterus and Pterygotus. Both of these possess the 
peculiar trilobitic head-shield, and may, therefore, supply useful informa- 
tion concerning this species. 
But the general outline of the fossil being semi-elliptical, does not well 
agree with that of Lémulus, and its fossil allies, which is semicircular. 
Limuloid forms descend to us from Silurian days, but they all present a 
semicircular head-shield similar to that of the living king-crab, Limulus 
Polyphemus, or Moluccanus, ‘of the east coast of America, and the Molueca 
islands. The same form of head-shield characterizes all the fossil genera 
allied to Limulus — Hemiaspis, Bunodes, Huproops, Belinurus, and Haly- 
cine. It is, consequently, impossible to refer our specimen to the dagger- 
tailed family of Xyphosurans. 
Not better does the outline of the head agree with that of the rounded, 
oblong head-shield of Pterygotus and Burypterus. Yet, in some respects, 
it reminds us of these. But the discrepancy is too great to allow of its 
reference to any established genus of the Burypterids. This will be evi- 
dent on an examination of the accompanying outlines. 
The eyes being undiscoverable in the fossil, the important evidence 
which they might afford towards settling its relationship is not available, 
but very important and conclusive testimony is derived from the markings 
on the surface of the carapace. Beside the wrinkles or tubercles men- 
tioned above, the crest is covered with small, delicate, crescentiform sculp- 
ture, resembling that which is characteristic of the Eurypterids, and a 
representation of which is given in the plate. 
