6 University of (.California Puhlications in Zoology [Vol. 13 



the carapace and the presence or absence of dorsal processes on cer- 

 tain of the abdominal segments. 



Key to the Species op the Genus Euphausia 

 1. Two denticles on the lateral margin of the carapace recurva 



1. One denticle on the lateral margin of the carapace 2 



2. No dorsal keel or process on abdominal segments tlirce to five pacifica 



2. A well-defined process on the dorsal posterior margin of the third abdominal 



segment ffH^ba 



Our collections contained but one animal, a female, which .shows 

 the two denticles, and it is provisionally referred to the following 

 species. 



Euphausia recurva Hansen 



PL 2, fig. 30 

 Euphausia recurva Hansen (1905b), p. 13. 



The specimen agrees closely with the description given by Hansen, 

 practically the only difference being that the leaflet on the first joint 

 of the antennule curves forward; the structure of the second joint is 

 as described by Hansen. In E. mutica (Hansen, 1905b, p. 14; 1909. 

 p. 93, pi. 14, fig. la) the leaflet curves forward, but the second joint 

 of the antennule is without a slender spine-like process. It is difficult 

 to estimate the value of such characters, but the structure of the second 

 antennular joint is of specific importance according to Hansen (1909, 

 p. 94). 



The length of the specimen is 12 mm. 



The second group which Hansen has formed among the species 

 of Euphausia is composed of those with a single lateral denticle and 

 without a dorsal process on the third to the fifth abdominal segments 

 (Hansen, 1911, p. 24). One species of those in the San Diego Region 

 is found in this group. 



Euphausia pacifica Hansen 



PI. 1, figs. 9, 14; pi. 2, figs. 18, 19, 23, 27, 29 

 Euphausia pacifica Hansen (1911), p. 28, fig. 10; (1913), p. 174. 



The anterior part of the carapace is not produced into a rostrmn, 

 though, seen from above, the margin is somewhat obtuse (pi. 1, figs. 

 9, 14). The eyes are spherical and unusually large. The first joint 

 of the antennule has in each sex a strong pointed process, at the an- 

 terior end on the dorsal side, which is directed forward (pi. 2, fig. 29) ; 



