30 



BULLETIN' 15 8, UNITED STATES NATIONAL MUSEUM 



rical; first antennae just reaching the caudal rami; inner margin of 

 fifth basipods armed with setae. Outer margin of second segment 

 of second exojDod with a deep notch at its proximal corner, armed 

 with a spine. Total length, 2.4^2.85 mm. 



Male. — Head fused with first segment; first antennae curved in 

 the form of an S, and a little longer than in the female. Eight 

 fifth leg very short, endopod 3-segmented, without setae and tipped 

 Avith two spines; exopod 3-segmented, without setae, but with a 

 process on the outer margin of the middle segment, shaped like a 

 slender finger. Left fifth leg without an endopod, the second 

 basipod segment greatly elongated, the exopod enlarged and 3-seg- 

 mented, the basal and second segments armed with long, sharp- 



FiGUEB 14. — Undinula vulgaris: a. Second segment of second exopod; 6^ fifth 

 legs of male ; c, fifth leg of female 



pointed, curved claws, the terminal segment tipped with a wormlike 

 process. Total length, 2.25-2.5 mm. 



Remarks. — This species, like the preceding one, prefers the trop- 

 ical parts of the ocean, but goes north in the Atlantic at least to 

 latitude 41° N. Although it is very cosmopolitan and is found in 

 all the oceans, the present is the first record of its occurrence on our 

 American shores. The highly modified fifth legs of the male, the 

 elongated left fifth exopod of the female, and the peculiar invagina- 

 tion of the second exopod in both sexes furnish convenient characters 

 for the identification of the species. 



Genus EUCALANUS Dana, 1852 



Head triangular, often elongated and fused with the first segment ; 

 rostrum produced into threadlike filaments; first antennae reaching 

 beyond the caudal rami, sometimes unequal in length, with colored 

 plumose setae at their tips ; endopod of second antennae longer than 

 exopod. Exopods of first four pairs of legs 3-segmented, first 

 endopod 2-segmented, the next three 3-segmented; fifth legs lacking 

 in female, uniramose in male, one lesr sometimes lacking. 



