418 PROCEEDINGS OF THE NATIONAL MUSEUM. yql. xxxiu. 



visible in dorsal view. Dorsal plates of the fourth segment consider- 

 ably enlarged, wider than the genital segment and covering its anterior 

 third or two-fifths, thoroughly fused with only a broad and very 

 shallow posterior sinus. 



Genital segment elliptical, one-fifth longer than wide; posterior 

 lobes broad and evenly rounded, with a shallow median siaus. 



Sixth segment plate small, its margin forming four-fifths of a per- 

 fect circle, the remaining fifth narrowed into an anterior stem or neck 

 where it joins the genital segment. It projects behind the lobes of 

 the genital segment for a half or two-thirds of its length. Anal 

 laminse rather narrow and slender, as long as the sixth segment plate, 

 acute at the tips and armed with two or three small spines irregu- 

 larly placed on the inner margin; wings entirely lacking in the adult. 

 Ventral plate of the abdomen much wider than the sixth segment 

 plate, its posterior margin usually evenly rounded. 



First antennae slender, the basal joint three times the length of the 

 terminal, its distal end enlarged, the anterior margin and corner 

 evenl}^ rounded and well armed with setae; terminal joint club- 

 shaped, with a tuft of setae at the tip. 



Second antennae slender, the second joint with a small fleshy lamina 

 on its ventral surface, the terminal claw short and weak. 



First adhesion pads elliptical, three-fourths longer than wide; 

 second pair obovate, one-half longer than wide, but much shorter 

 than the first pair; fourth pair elliptical, a little more than twice as 

 long as wide, and longer than the first pair. 



Mouth-tube of the usual shape, narrower and longer than in 

 hicolor; mandibles like those of smitJiii; second maxillae short and 

 broad, the basal joint twice as wide as long, the second joint as wide 

 as long and ending in a slender and sharp spine which is nearly 

 straight. First maxillipeds slender, the basal joint half as long again 

 as the terminal ; the latter armed with a terminal curved claw, nearly 

 as long as the joint itself, a shorter and straighter accessory claw, 

 toothed along both margins, on its ventral surface, and a short and 

 straight, spine on the inner margin, both the latter being inserted at 

 the base of the terminal claw. 



Second maxillipeds much swollen, armed with a pair of knobs 

 acting like forceps; knobs oblong, the ends where they come together 

 being flattened and corrugated. 



Basal joints of the swimming legs increasing in size from in front 

 backwards, all biramose and the rami two-jointed, but the joints on 

 the fourth pair are thoroughly fused, and the jointing is only indi- 

 cated by marginal notches. The arrangement of the spines (there 

 are no true setae) on the different legs is as follows: First exopod, 1,5; 

 endopod, 0, 3; second exopod, 1, 9; endopod, 0, 5; third exopod, 1, 4 

 to 8; endopod, 0, 3; fourth exopod, 1, 3 to 5; endopod, 0, 0. The 



