45 



described and figured in the last number of this Bulletin. The two 

 joints of the antennae measure, resp., 2 l A and iH inches in length, 

 with a width of a little more than one-eighth of an inch for the an- 

 terior, and a trifle less for the posterior joint. Judging from their 

 thickness, they must have been cylindrical in shape. The whole 

 length of the appendage is 5H inches. The specimen shows also 

 the fragmentary parts of ten body segments, one swimming-foot and 

 three anterior feet. These latter are more slender and have longer 

 joints than the corresponding feet in Eurypterus. The surface 

 markings of the body consist on the first six segments, of small scales, 

 and on the remaining four, of small, irregularly scattered pustules. 



Length of the ten segments, 7K inches. Geological position 

 and locality: the water-lime group near Buffalo. 



If we take it for granted that the above described chelate ap- 

 pendage did belong to the body, which, to some extent covered it, 

 and of which a portion had to be chipped away to expose the ramus, 

 then these antennas have been the largest appendages of the genus, 

 longer even than the swimming-foot. 



There cannot be any doubt that the body was a part of a Ptery- 

 gotus, on account of the peculiar surface markings, the shape of the 

 anterior feet and the swimming-foot, the latter had to be cut away, 

 together with a part of the body; and, however opinions may differ 

 as to the relation in which the " chelate antennse " stood to the body, 

 we must admit that this organ existed in the shape described and 

 figured for P. bilobus. {Palaeontology of New York, Vol. III., 424.) 



All the above described specimens are in the museum of the 

 Society. 



