83 Canadian Arctic Expedition, 1913-18 
shown in Pl. III, 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 expodite, 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, Pl. III, fig. 9, the spines of the first basal seg- 
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 
Pl. III, 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 Pl. ITI, 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 ITI, figs. 11, 12 and 14. Plate IV, figs. 1 and 5. 
This corresponds, in general structure, to others of the viridis type. The 
antenne of the female equal in length the first segment of the cephalothorax. 
The abdomen is shown in PI. IIT, fig. 11, and the furca enlarged, in Pl. ITI, fig. 14. 
The furea is finely ciliate on its inner border. The lateral seta is situated at 
three-fourths of the length of the furca. Of the terminal sete the outer is two- 
