662 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxviii. 



other, backward, and in the adult females usually forward, until the} 7 

 finally fuse into a single plate or lamina. 



The genital segment, seen from below, is about half the width of the 

 carapace, and is ovate in shape, narrowing rapidly toward the poste- 

 rior end. The sides are very evenly rounded and the dorsal lamina 

 which covers the entire upper surface projects considerably beyond the 

 lateral margins, and extends backward on either side of the abdomen 

 in a broad, flattened lobe. These lobes are about one-third the width 

 of the lamina at the point where they arise and each is tipped with a 

 stout spine. The sinus between them is deep and almost a perfect 

 semicircle in outline, leaving- exposed the terminal half of the abdomen. 

 This latter is small, only one-fourth the length of the genital segment, 

 and composed of a single joint. Its base is concealed beneath the pos- 

 terior edge of the dorsal lamina, which covers both the free and geni- 

 tal segments, and it tapers strongly posteriori} 7 . It is tipped with a 

 pair of small and narrow anal laminae, which are well separated and 

 armed with short setae. The egg strings are a trifle wider than the 

 abdomen and about as long as the carapace; each contains from seventy 

 to eighty eggs. 



Of the appendages the first antennae are large, more than half the 

 length of the frontal plates; the two joints are the same length, the 

 terminal one being narrow and club-shaped. 



The second pair are of medium size; the basal joint is not much 

 swollen and is furnished on its dorsal surface, at the inner corner of 

 the distal margin, with a circular plate covered with short and stiff 

 bristles. The terminal claw stands at right angles to the basal joint 

 and is sharply bent near its tip. 



The first maxillae are small, slender, and strongly curved; the second 

 pair are also small and are cut beyond the center, the inner branch 

 being considerably smaller than the outer one. The mandibles are 

 strongly curved at the tip, with about a dozen large serrate teeth along 

 the inner margin of the curve. The first maxillipeds have a small chitin 

 lamina inserted in the inner margin of the terminal joint near its cen- 

 ter. They" terminate in three claws instead of the usual two; the 

 inner one is considerably longer than the two outer ones, which are 

 about the same length. The outer claw has a pectinate edge along its 

 outer margin. ,, 



The second maxillipeds are small, the terminal claw not more than 

 a third the length of the basal joint, with a long and slender accessory 

 spine inserted near its base. 



The f urea is small, the base longer than the branches and somewhat 

 swollen, with a large rectangular foramen. The branches are short, 

 well separated, a little divergent, and blunt at the tips. 



The first swimming legs have a large plumose seta on the posterior 

 margin of the basal joint and a stout spine at its distal corner. There 



