127 



the essential specific character that immediately distinguishes R. tricus- 

 pidata from all others of the same genus; namely, the peculiar strncture 

 of the second pair of gnathopoda. The head is larger in the female, but 

 the general shape is the same; the thorax is shorter and deeper, and 

 the last segment is much narrower ; the abdomen is also narrower. The 

 character of the superior antennae is the same in both, except that in the 

 female they are much smaller, and the joints are more plainly visible. The 

 inferior antennae, however, are quite different. They do not extend at 

 all, or very slightly, beyond the anterior margin of the head. The first 

 basal joint is very short, and broader than the following; the second long, 

 and reaches nearly to the anterior margin of the head; the third joint 

 is rudimentary ; and the fourth is apparently obsolete. The flagellum is 

 small, about one-third the length of the first joint, lanceolate in shape, 

 and with two or three stout cilia at its apex. The shortening is chiefly 

 due to the diminished length of the first joint of the peduncle. The pos- 

 terior ijair of thoracic legs are slenderer and shorter than the preceding 

 pairs. The peduncles of the anterior abdominal appendages are ovate, 

 instead of being elliptical; the posterior appendages show no differ- 

 ences. 



Length of male .30 inch ; of female, .25 inch. 



I cannot think that these differences are anything more than sexual, 

 OQ account of the strong specific resemblance there is between the speci- 

 mens. Carcinologists generally have adopted the conclusion that Les- 

 trigonus is the male sex of Eyperia, but at no time, I think, has there 

 been sufficient evidence at hand to justify this conclusion. I know no 

 better reason for the supposition, than that they are occasionally found 

 associated together, joined with the fact that certain others of the Hy- 

 peridea show a similar sexual difference ; namely, in the length of the 

 antennae. In the Lestrigonus, however, there is not only a difference in 

 the length, but a total change in the structure of the antennae. What is 

 here held to be a male bears no resemblance to a Lestrigonus^ but has 

 all the generic characters of a Hyperia; and, while there is a modified 

 growtli, as in the former genus, the development of the antennae is the 

 same in both individuals. 



Young. — Head narrow, quadrilateral. Superior antennae short and 

 stout, and situated nearer the superior margin of the head than in the 

 adult; the first basal joint as long as the three terminal ones; the sec- 

 ond longer than the third, and their breadth less than that of the first; 

 the fourth joint small, and either rounded or broadly triangular, with 



