65 Canadian Arctic Expedition, 1913-18 
in Pl. II, fig. 8, differ from the preceding description only in the somewhat greater 
length of the right foot. 
This species was collected in ponds on Herschel island, Yukon Territory, 
August 14, 1914, and again July 30, 1916. 
Genus Diaptomus. 
Diaptomus bacillifer Kolbel. 
Plate III, figs. 1-5. 
Up to the present time no species of Diaptomus found on the American 
continent has been considered identical with those of Europe or Asia. There- 
fore a good deal of care was used to make certain that the identification of 
this species was correct. The determination is based on the original description 
of Kélbel, 1884, supplemented by the later descriptions, especially those of 
Sars and Schmeil. 
Kélbel gave as the length 1.5 to 2 mm. Sars, 1903, states that the female 
are 1.8 mm. and the males 1.4mm. De Guerne and Richard, 1889, make the 
length from 1 mm. to 1.5 mm. Of the specimens of these collections, one 
set of four females averaged 1.31 mm. Another set of five females averaged 
1.45 mm. Five males averaged 1.295 mm. These measurements correspond 
very well to those of the European individuals. In our specimens the antenne 
extended to the end of the first abdominal segment and in some cases nearly 
reached the furca. Kdélbel says that the antenne reach ‘iiber die furca.” 
DeGuerne and Richard make the antenne almost reach the furca. Sars, 1903, 
says that the antenne reach to about the middle of the genital segment, but 
Sars, 1898, says that the antennz reach the end of the first abdominal segment. 
The last cephalothoracie segment is produced backward on the sides, and each 
wing is armed with two minute spines, as shown in Pl. III, fig. 1. The abdomen 
of the female, shown in PI. III, fig. 2, in its general form corresponds very closely 
to the figure in Sars 1903. The first segment is longer than the remainder of 
the abdomen including the furce, is moderately dilated on the sides, decidedly 
dilated in front, and bears a small acute spine on each side, these spines ordinarily 
being slightly turned backward. The second segment of the abdomen, in our 
specimens, was about one-half the length of the third; these proportions differ 
slightly from those of the European specimens, but no more than what might 
be considered a reasonable variation; moreover, such measurements are never 
very exact. The furcal rami are nearly as long as the two preceding segments. 
Kolbel states that they are as long as the last segment and one-half the pre- 
ceding; he also says that the furcal rami are ciliated on both the inner and outer 
borders; this was true of some of our specimens, but in others, as in the one figure 
in Pl. III, fig. 2, only the inner border was ciliated. 
The fifth foot of the female, Pl. ITI, fig. 3, has a weak spine on the first basal 
segment, and a delicate seta on the second segment. The exopodite is three- 
segmented. The second segment bears a spine on its outer distal angle, and 
the third segment is terminated by two spines, the inner being somewhat 
the stouter. The endopodite is one-segmented in our specimens. In the figures 
of Kélbel, 1884, and Sars, 1903, it is two-segmented. In the figure of DeGuerne 
and Richard it is one-segmented. Apparently the endopodite may be either 
one or two segmented. The length of the endopodite is stated by Schmeil, 
1893, to be variable. Sars, 1898, states that it is less than one-half of the 
first segment of the exopodite, and in 1903 he says that it is much shorter 
than that segment. In our specimens it was about one-half the length of the 
segment. 
The appendage of the antepenultimate segment of the right antenna of 
the male is straight and about equals in length the penultimate segment. This 
