554 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 94 



reaching only the middle of the second thoracic segment, leaving all 

 the rest of the thorax uncovered, whence the specific name. The 

 cephalic area is ovate and 70 percent of the carapace length ; the com- 

 pound eyes are proportionally large, well separated and removed from 

 the anterior margin. The respiratory areas are peculiar; the smaller 

 one is circular in outline and lies inside the larger one near the anterior 

 end of the latter. This anterior end is narrowed outside the smaller 

 area and abruptly widened behind it and curved backward and in- 

 ward, the posterior end enlarged somewhat. The second and third 

 thoracic segments are the same width but the third is slightly the 

 longer. The fourth segment is both shorter and narrower and ite 

 lateral margins are strongly convex. The abdomen is elliptical, one- 

 half longer than wide and about one-fifth the total length. The 

 posterior sinus is a third of tlie abdomen length and the caudal rami 

 are lateral, each upon a shoulder of the lateral margin of the sinus at 

 its center. The seminal receptacles are circular, close together and 

 close to the anterior margin of the abdomen. They are partially ob- 

 scured in dorsal view but are plainly visible on the ventral surface. 



In the first antennae the spine on the anterior margin is stout 

 and curved inward while the lateral spine is long and slender and 

 bent into a half circle. The curve of this spine extends considerably 

 beyond the tip of the flagellum, which is 2-segmented and tipped 

 with three small setae. The second antennae are 4-segmented, the 

 posterior spine on the basal segment slender and acuminate. The 

 supporting rods in the margin of the sucking disks are close together 

 and 6-segmented. The basal segment is cylindrical and as long as 

 the other five combined, which are beadlike, tapered distally, and 

 tipped with a tiny spine. The pad on the basal segment of the 

 maxilliped carries three slender acuminate spines and the end seg- 

 ment is armed with three small claws. The swimming legs reach 

 beyond the lateral margins of the carapace, the first two pairs bearing 

 flagella. The proximal segment of the fourth basipod has a posterior 

 process without a heel, but with an acuminate toe which projects 

 well beyond the lateral margin of the abdomen. Total length, 2.30 

 to 2.55 mm. Carapace, 1.70 mm. long, 1.50 mm. wide. 



Male. — Similar to the female but a little larger, the carapace ellip- 

 tical and broadly rounded both anteriorly and posteriorly, one-fourth 

 longer than wide, and reaching the posterior margin of the second 

 segment. The cephalic area is as long as in the female, the pos- 

 terior sinus equally broad and shallow. The second and third tho- 

 racic segments are about the same length with nearly straight sides, 

 the fourth segment is narrower and shorter with convex sides. The 

 abdomen is one-half longer than wide, its lateral margins more convex 

 than in the female. The testes are elongate-elliptical and reach 

 nearly to the base of the posterior sinus, which is one-fourth the 



