230 Illinois State Laboratory of Natural History. 



dorsal surface. First pair of antennae 23-segmented : right 

 male antenna geniculate between the 18th and 19th seg- 

 ments, and the 19th and 20th segments ankylosed. Second 

 pair of antennae, mandibles, and first, second, and third 

 pairs of maxillae as in Diaptomus, but stouter. All the swim- 

 ming legs biramose, with three-segmented inner and outer 

 rami; armed with stout seta?. In the female the legs of the 

 fifth pair are alike, biramose, the rami three-segmented, the 

 inner ramus the shorter. Fifth pair of legs of male bira- 

 mose, dissimilar. Both rami of left leg three-segmented, the 

 inner ramus the shorter. Outer ramus of right leg two- 

 segmented, the inner three-segmented and like the inner 

 ramus of the left leg. Egg-sac obovate. 



Osphranticum labronecturn Forbes. 



Osphranticum labronecturn, Forbes, '82, p. 645, PI. VIII., Fig. 24. 28. 

 29; PL IX., Fig. 1, 2, 4. 5, 7, 9. 



Potomoichetor* fucosus, Herriek, '82. p. 224, PI. II., Fig. 12-14: Pi. 



III., Fig. 1-8. 13. 14. 

 Osphranticum labronecturn, Herriek, *84. p. 134, PJ. Q2, Fig. 1-8. 13. 14. 

 Osphranticum labronecturn, Herriek, "87. p. 12. 



Osphranticum labronecturn, de Guerne et Richard. 89b, p. 149, Fig. 1 . 2. 

 osphranticum labronecturn, Herriek and Turner, *9">, p. 86. PL XII.. 



Fig. 1-8, 13, 14; PL LIX., Fig. 7, 8. 



Of medium size, body compact, widest before the middle. 

 Ceplialothorax composed of six segments decreasing gradu- 

 ally in length from before backward ; first two segments con- 

 fluent above, the last segment slightly produced at the angles 

 into bluntly-rounded points, but unarmed. Abdomen (furca 

 included) composed of five segments, decreasing in length 

 from before backward. Furcal rami, however, slightly longer 

 than the preceding segment and about twice as long as wide ; 

 hairy on the inner margin and armed with five long plumose 

 seta? of which the second from within is the broadest and 

 longest, the middle one being next in length, and the other 

 three subequal ; dorsal surface of each ramus armed near 

 the inner apical angle with a delicate smooth seta. Abdo- 

 men of male composed of six segments : the first shorter 



■Spelled Polamoichetor in Merrick's subsequent refereints. 



