27 



processes ; the sixth joint is articulated to the fifth in the same 

 manner, and surpasses it a little in length ; the seventh joint 

 dilates somewhat, is as long as the five preceding joints together, 

 and has on its exterior margin a triangular indentation with the 

 apex a little anteriorly ; this is formed by the prolongation of 

 the joint anteriorly, and by a triangular piece attached by a 

 soldered suture line posteriorly ; into this indentation the ovate 

 shaped palette is articulated. No terminal palette is present. 



The surface of the first joint is covered with scales, and 

 assumes a pustulose character on the second and third joints. 

 Length of the whole swimming foot is 6 1-4 inches. 



A fragment of a chelate antenna is exposed on the ventral 

 side, and although it demonstrates clearly that it really was the 

 largest of all the appendages of the genus Pterygotus ( B. B. S. 

 N. S., Vol. iv., p. 17,) we are as yet in the dark about its place of 

 attachment to the body. 



Length of whole specimen 15 inches ; greatest width 7 1-2 

 inches. 



Found in the Waterlime group near Buffalo, N. Y. 



PTERYGOTUS BILOBUS, Huxley and Salter. 



A fragment consisting of eight posterior segments, and the 

 tail has been found, which presents no special characteristics of 

 the body' excepting the equal length of the segments. The inter- 

 est lies in the caudal appendage. Although the tail of this 

 specimen differs in its proportions as well as in size from that of 

 the above named species, as figured in the Palaeontology of 

 New York, Vol. in., p. 424*, it can well be referred to it for the 

 present. This tail is ovoid, and has a length of 1 3-4 inches and 

 a width of 3 1-4 inches. It is divided in the middle of its poste- 

 rior margin by a deep indentation of about 1-2 inch. A line which 

 divides the tail into two lobes for two-thirds of its length can be 

 seen from this indentation running anteriorly. 



Length of the whole specimen 13 inches. There are no sur- 

 face markings ; the segments are too fragmentary for a detailed 

 description, but they show that the animal must have been com- 



