562 PROCEEDINGS OF THE NATIONAL MUSEUM vol. lis 



Lake 8 had this spine less developed than in all other specimens, its 

 length being less than half the segment). 



Taxonomy. — E. arctica is easily distinguished from other species of 

 the genus by the combination of characters summarized in the def- 

 inition. It does not appear to be closely related to any known species 

 but can be assigned on the basis of characters of the antennules and 

 female leg 5 to a broadly defined group that includes E. composita and 

 E. gracilicauda. Leg 5 is distinctive in both sexes — that of the female 

 in the unusually long extension of the inner process of exopod 1 and 

 that of the male in the lobes and processes of the basal segments and 

 the structm'e of exopod 2 of both legs. 



Leg 5 of the male is also distinctive in copepodid stage V. No other 

 species illustrated in literatm'e or observed from North American 

 fresh and brackish waters has long apical spines (as shown in fig. 3^) . 

 The specimens from Umiat and Noatak can therefore be assigned to 

 this species, even though adidts were not observed. It is also possible 

 that the inner process of leg 5 of stage V female is longer than in other 

 species of Alaskan Eurytemora, but more study is required to deter- 

 mine this. 



OCCUERENCE IN CaPE THOMPSON REGION 



Lake 4 (type locality; see above, p. 554). — Only 33 individuals were 

 captured in both quantitative and qualitative open-water and littoral 

 samples taken on 17 dates between June 24 and November 7, 1960; 

 no specimens occurred after September 8 nor in mid- and late winter 

 samples in 1961. The species was present in open-v/ater samples 

 taken in the deepest part of the lake on 10 of the 17 dates in 1960 

 and in 1 littoral sample (June 24). Of the total 11 dates, only 1 

 specimen occiu-red on 4 dates, from 2 to 6 on 6 dates, and 9 adults, 

 the largest number, were taken on the remaining date. From July 21, 

 specimens were in copepodid stages V and VI. Stage VI (adults) first 

 appeared on July 14 and was the only one present in samples of late 

 August to mid-September. Of the 10 adult females, none carried 

 ovisacs or spermatophores. Three of the 6 males taken on August 27 

 and September 8 had spermatophores attached to the apex of left leg 5. 



Summary of number of specimens of copepodid stages (C) collected 

 on the 11 dates of 1960: 



June July August September 



4 19 27 8 14 



2 



2 4 1 



5 1 



