WATER LIME GROUP. 
419 * 
This is the only carapace which I have seen, where the eyes are marginal. In the 
form and appearance of the carapace, the specimen resembles others of the genus; 
but I am not aware that the central tubercle, with the eye-like spots, has been 
noticed in Pterygotus. A similar feature has been observed in Eurypterus , though 
not seen in all the species of the genus. 
Fig. 8. The carapace, natural size. 
Fig. 8 a. A small portion enlarged, to show more distinctly the oblong tubercle, and the 
small eye-like points which are faintly visible to the naked eye. 
Geological position and locality. In the Waterlime group : Wlieelock’s hill, 
Litchfield, Herkimer county. 
Pterygotus osbomi (n.s.). 
Plate LXXX A. Fig. 9. 
Carapace unknown. Body elongate. The four anterior joints of the thorax 
have a width of about four times their length. The first segment shows 
the point of attachment for the thoracic appendage, as in Eurypterus. 
Postoral plate elongato-cordiform. First joints of the natatory feet 
rhomboid-ovate, and toothed on their inner margins ; the four anterior 
feet slender, with long joints ; the basal joints broad, with long spine¬ 
like teeth. The entire length of the cephalic portions, and the four first 
joints of the body, is about three inches. 
Fig. 9. A figure of the specimen, natural size. A reference to tire parts of Eurypterus will 
explain the relations of the parts of this figure. 
Geological position and locality. In the Waterlime group : Waterville, Oneida 
county. 
CERATJOCARIS. 
The posterior or caudal spines of this crustacean have been known in our 
rocks from fragments in the Clinton and Niagara groups, as well as in the 
Waterlime group. Until their true character was pointed out by Professor 
M c Coy of London, these fossils were regarded as the defensive spines of 
fishes, and were thus described. A species from the Niagara group has 
been described in the second volume of the Paleontology of New-York, 
