164 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.41. 



of hairs and two ciliated setae; upon exopodite, one short and one 

 long seta; anterior or outer branch of endopodite encircled with 

 three rows of short stiff hairs, three strong terminal setse, one of 

 them two-segmented; the posterior or inner branch of endopodite 

 plainly three-lobed, each lobe bearing, respectively, beginning 

 anteriorly, two short heavy ciliated setae or spines, three still stronger 

 ciliated spines, and four more delicate two-segmented setae. The 

 second to fifth legs almost identical with those of Ophryoxus, but 

 with the geniculate setae upon maxillary processes of third, fourth, 

 and fifth very strongly developed. Sixth leg asymmetrical; on lower 

 posterior border a protuberance with two fasciculi of long cilia, 

 ventrally a row of cilia; on anterior border cilia, fine and numerous 

 below, sparse and stronger above. 



The postabdomen slender and triangular, the two converging 

 borders irregularly sinuous; about three short spines upon the flexible 

 basal part of the superior or posterior border; anal setae two, sparsely 

 ciliated; further armature lacking, except for double row distally of 

 about eleven small obsolescent spines, and laterally two or three fas- 

 ciculi of five to eight delicate cilia each, forming a line approximately 

 parallel to the posterior border. Terminal claw long, nearly or quite 

 half the length of postabdomen, evenly but slightly curved; at base 

 two small subequal teeth, the distal larger; externally at base a row 

 of six small denticles, distal to which the row is continued to the tip 

 with delicate cilia; internally there is a similar row, but with a group 

 of larger cilia instead of denticles; on convex border a row of cilia, 

 distinct at base, but smaller and appressed to the claw toward the 

 tip. 



Intestine flexed once upon itself and coiled once in the body; he- 

 patic caeca small; rectum large without caeca. 



Male. — Immature males only have been collected. The most 

 advanced specimens are assumed to show most clearly the male 

 structure. 



Form, proportion, and general structure essentially as in females 

 of equal development, with the following distinctive details. First 

 antennae or antennules with conspicuous offset or prominence as in 

 Bosmina, on anterior margin, one-fourth distance from base, the angle 

 of which bears a seta reaching well toward end of antennule. The 

 anterior border of antennule distal to offset, with five to eight slight 

 notches or traces of segmentation in youngest specimens. Second 

 antennae or antennae proper with seta upon the proximal segment 

 of lower or inner ramus reaching just to or beyond the seta upon the 

 penultimate segment, these two setae being distinctive for males. 



The hook of first thoracic leg strong, slightly curved. The number 

 of obsolescent spines or spicules of posterior or distal border of 

 postabdomen reduced to about three. In some of the most advanced 



