312 



BULLETIN 15 8, UNITED STATES NATIONAL MUSEUM 



Color. — Body very transparent, with ferruginous pigment vari- 

 ously distributed through the cephalic segment, especially in the 

 region around the mouth. The same pigment sometimes forms 

 spots symmetrically arranged in the thorax, the abdomen, the long 

 setae of the first antennae, the furca, and the swimming legs. Other 

 individuals are quite colorless except for the ruby-red eye. 



Female. — Rostrum turned downward but at the same time ex- 

 tended forward far enough to render it visible in dorsal view ; caudal 

 rami shorter than the anal segment but three times as long as wide ; 



setae on the outer margin and the tip of 

 each ramus densely plumose and highly 

 colored. First antennae reaching the anal 

 segment; outer margin spines of the three 

 exopod segments of the first four pairs 

 of legs: 1, 1, 2; 1, 0, 2; 1, 0, 1; 0, 0, 1; re- 

 spectively. The setae on the basipods of 

 the second, third, and fourth legs and on 

 the sides of the fifth metasome segment 

 project at right angles to the body axis 

 and are visible dorsally. Total length, 

 1-1.5 mm. 



Male. — Rostrum lacking; second abdom- 

 inal segment about as wide as long, anal 

 segment the same length as each of the 

 two preceding segments. First antennae 

 twice geniculate; the first segment beyond 

 the promixal elbow sheathing the base of 

 the segment in front of it, the first segment beyond the distal elbow 

 with a semicircular process on its inner margin. End segment of 

 first and fourth exopods with two outer spines, of second and third 

 exopods with three outer spines. Total length, 0.75-1 mm. 



Remarks. — This species may be recognized by the long and highly 

 colored plumose setae mentioned in the foregoing descriptions. It 

 is apparently a pelagic species and chiefly tropical in its distribution, 

 and comes into the area around Woods Hole as a straggler from the 

 south. 



OITHONA SPINIROSTRIS Clans 



FiGxmB 188 



Oithona spinirostris Claxjs, Die frei lebenden Copepoden, p. 105, pi. 11, 1863. — 

 Saes, Crustacea of Norway, vol. 6, p. 6, pis. 1, 2, 1913. 



Occurrence. — Thirty specimens, including both sexes, were cap- 

 tured in a surface tow, March 19, 1920, southeast of Marthas 

 Vineyard. 



FiGORB 187. — Oithona plumi- 

 fera: a, Male, dorsal ; b, 

 female, fifth leg 



