8j Canadian Arctic Expedition, 1913-18 



shown in PI. Ill, fig. 8, the spine of the first basal segment is rather large. The 

 second basal segment bears the customary lateral seta. The exopodite consists 

 of three segments. The second segment bears a small spine at its outer distal 

 angle; the hook is of the ordinary form. The third segment, which is distinctly 

 separated from the second bears two spines. The endopodite is one-segmented, 

 as long as the first segment of the expedite, and is terminated with two rather 

 long spines. 



The antepenultimate segment of the right male antenna, shown in PI. III. 

 fig. 7, bears a nearly straight appendage, which is as long as the penultimate 

 segment. In the male fifth foot, PI. Ill, fig. 9, the spines of the first basal ><<:- 

 ments are small. The second basal segment of the right foot is about equal in 

 length and breadth ; it bears a minute hyaline cuticular appendage near its inner 

 proximal angle, and near the inner distal angle a pronounced process which is 

 serrate on its outer border. This is shown from the ventral side, enlarged, in 

 PI. Ill, fig. 13. The endopodites are two segmented. The left foot reaches 

 nearly to the end of the second segment of the exopodite of the right foot. 



Average length: females 3.08 mm., males 2.72 mm. 



This was found in a collection from a pond on Herschel island, made on 

 August 14, 1914. 



The female can hardly be distinguished from D. shoshone. The only 

 differences are the possibly "heavier spines of the first segment of the abdomen 

 and of the first basal segments of the fifth feet and the two-segmented endopodites 

 of the fifth feet. 



It is in the fifth feet of the male that the species distinction is made. The 

 greater length of the left foot and the armature of the second basal segment of 

 the right foot warrant us in separating D. arcticus from shoshone. Material of 

 D. shoshone has been examined from Yellowstone lake, from Corona, Irwin, and 

 Pike's peak, Colorado, from Nioche valley in the Wasatch mountains, Utah, 

 and Lake McDonald, St. Paul's island, Alaska. In none of this material is shown 

 the peculiar armature of the second basal segment of the male right fifth foot 

 of D. arcticus; it may be noted, however, that in the specimens from Lake 

 McDonald and Nioche valley there is, near the inner proximal angle of this 

 segment a very minute cuticular ridge, which might be considered as a rudiment 

 of the hyaline process found in D. arcticus. A constant structure in D. shoshone. 

 too, is a small spine on the dorsal surface of the second segment of the exopodite 

 at about one-third its length. This spine does not appear in D. arcticus. 



D. wardi Pearse, is very closely related to these two forms. Juday and 

 Muttkoswki, 1915, consider D. wardi a variety of D. shoshone, but until it is 

 clearly shown that there are connecting forms, it would seem well to retain the 

 species name. For the sake of comparison, the male fifth foot of D. wardi, from 

 St. Paul island material, is shown in PI. Ill, fig. 10. It differs from D. shoshone 

 in having a distinct hyaline . process near the proximal inner angle of the second 

 basal segment, and in not having the spine of the dorsal surface of the second 

 segment of the right exopodite, and it has no trace of the pronounced process 

 of the inner distal angle of the second basal segment which is seen in D. arcticus. 



Genus Cyclops. 



Cyclops magnus, n. sp. 

 Plate III, figs. 11, 12 and 14. Plate IV, figs. 1 and 5. 



This corresponds, in general structure, to others of the viridis type. The 

 antennae of the female equal in length the first segment of the cephalothorax. 

 The abdomen is shown in PL III, fig. 11, and the furca enlarged, in PI. Ill, fig. 14. 

 The furca is finely ciliate on its inner border. The lateral seta is situated at 

 three-fourths of the length of the furca. Of the terminal setae the outer is two- 



