1914.] NATURAL SCIENCES OF PHILADELPHIA. 39 



The female first antennae consist of sixteen segments. Herrick 

 notes a similar form with seventeen joints, but this again I am unable 

 to verify. They extend a little beyond the posterior margin of the 

 first thoracic segment. The second, third, tenth, and thirteenth 

 segments bear unusually long, heavy, plumose setae. In the males 

 these spines, which correspond to those of the third segment in the 

 female antennae, are very conspicuous (PI II, fig. 7). When the 

 first antennae are folded under the body they protrude as shown in 

 the figure. This also occurs when the female aniemiap are folded 

 under the cephalothorax. The female antennae show an unusual 

 change of direction between the third and fourth segments, giving 

 the animal a characteristic appearance and making the females 

 resemble the males to the naked eye. On the fourteenth and fifteenth 

 segments of the first female antennae occur several characters that 

 may be sensory in function. The fourteenth segment bears a minute 

 sensory hair and a verj^ inconspicuous, transparent, hyaline plate 

 that contains about twelve coarse serrations (PI. II, fig. 11). The 

 fifteenth segment bears a smooth-edged hyaline plate of which the 

 distal end is club-shaped and protrudes considerably beyond the 

 anterior end of the segment. Forbes ('97) indicated the position 

 of this plate in his fig. 1, PI. XVI, of the first female antennae, but he 

 seems to have overlooked the character of the organ. In the figure, 

 the positions of the large setae of the fourteenth and fifteenth segments 

 are indicated. 



The armature of the three segmented swimming feet is very 

 constant. The setae and the apical spines are long and slender. 

 Forbes notes that "the distal segments of the third and fourth pairs 

 of legs turn inward in a way peculiar to this species." The inner 

 border of the distal segment of the inner ramus of all four pairs is 

 finely plumose. The feet armature is as follows: 



First pair — outer ramus, four spines, four setae; inner ramus, six 



setae. 

 Second pair — outer ramus, four spines, five setae; inner ramus, six 



setae. 

 Third pair — outer ramus, three spines, five setae; inner ramus, six 



setae. 

 Fourth pair — outer ramus, three spines, five setae; inner ramus, one 



seta, two spines, two setae. 



The lamellae connecting the swimming feet have a peculiar form. 

 PL II, fig. 10, shows this feature in the third pair. In the fourth pair 

 the place of the seta on the basal joint is taken by a short chitinous 



