2 



six appear to be made out on the specimen. The surface of the 

 cast is punctate with scattered triangular impressions. The cast 

 shows a widening of the terminal segment and no traces of a 

 spiniform process are exhibited. This portion of the fossil was 

 imbedded in the matrix, and seems to have been bent downwards 

 and outwards in the specimen. The greater flexibility of the 

 caudal segments may be inferred from their shape and position. 

 The specimen from which the above description is drawn was 

 found in the water lime group at Buffalo, N. Y., in the same bed 

 which has furnished us specimens of Earypterus lacustris. The 

 length of the entire specimen is two hundred and fifty millime- 

 tres; the greatest width of the body is one hundred and ten 

 millemetres. 



The interest which attaches to this remarkable Crustacean 

 arises from the discovery of a form which may be allowed to be 

 higher than Eurypterxis and Pterygotus from the peculiar differ- 

 entiation of the body expressed by the narrowness of its cephalo- 

 thoracic portion, and the sudden constriction of the terminal 

 segments. 



The accompanying photographic plate (I) illustrating the speci- 

 men, has been prepared by Mr. Alfred W. Simon of Buffalo. 

 The collection of the Buffalo Society of Natural Sciences owes 

 the specimen to the liberality of Mr. U. Cummings. 



