6j Canadian Arctic Expedition, 1913-18 



in PI. 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 Kolbel, 1884, supplemented by the later descriptions, especially those of 

 Sars and Schmeil. 



Kolbel gave as the length 1 . 5 to 2 mm. Sars, 1903, states that the female 

 are 1.8 mm. and the males 1.4 mm. 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 antennae 

 extended to the end of the first abdominal segment and in some cases nearly 

 reached the furca. Kolbel says that the antennae reach " liber die furca." 

 DeGuerne and Richard make the antennae almost reach the furca. Sars, 1903, 

 says that the antennae reach to about the middle of the genital segment, but 

 Sars, 1898, says that the antennae reach the end of the first abdominal segment. 

 The last cephalothoracic 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 PL 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 furcse, 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 III, 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 Kolbel, 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 



