36 



BULLETIN 15 8, UNITED STATES NATIONAL MUSEUM 



on the dorsal surface, these spines increasing in size posteriorly; 

 fifth legs without a seta on the second segment, and with a single 

 one, stout and curved, on the inner margin of the third segment, 

 distal to the center. Total length, 3.5-3.75 mm. 



Male. — Eight fifth leg uniramose, 3-segmented, and tipped with 

 a nearly straight claw ; left fifth leg biramose, endopod 2-segmented, 



the basal segment one- 

 half longer than the 

 terminal; exopod 

 nearly as long as the 

 endopod, 1-segmented, 

 and tipped with a long, 

 slender, and slightly 

 curved claw. Total 

 length, 2.5-2.75 mm. 



Remarks. — Though 

 this species has its 

 center of distribution 

 in the tropical portions 

 of the large oceans, as 

 noted by Bigelow, it 

 does occur rather fre- 

 quently within the 

 present area, and has 

 been found in consid- 

 erable abundance at one or two stations off Marthas Vineyard. It 

 can be recognized at once by the anchor-shaped frontal projection. 



Genus MECYNOCERA Thompson, 1888 



Head separated from the first segment ; fifth segment with rounded 

 posterior corners; first antennae more than twice as long as the 

 entire body, with very long setae at the tip; urosome 3-segmented 

 in the female, 4-segmented in male; none of the caudal setae elon- 

 gated; exopod of second antenna half as long as endopod; exopods 

 of first four pairs of legs 3-segmented, endopod of first pair 1-seg- 

 mented, of the other three pairs 3-segmented; fifth legs uniramose, 

 5-segmented in both sexes. The genus contains but a single species. 



Figure 19. — Rhincalanus cornutus: o. Female, dorsal; 

 I), fifth leg of female; c, male, fifth legs (r, right 

 leg) 



MECYNOCERA CLAUSI I. C. Thompson 



FiGUBE 20 



Mecynocera clausi Thompson, Journ. Linn. Soc. London, vol. 20, p. 150, pi. 11, 

 1888. — GiESBRECHT, Fauna und Flora des Golfes vou Neapel, vol. 19, p. 160, 

 pis. 5, 11, 35, 1892. 



Occurrence. — Six females captured at the surface outside of 

 Marthas Vineyard in the summer of 1915. 



