Freshwater Copepoda 53 
the body of the furca. PI. II, fig. 1 shows the furca enlarged. The antenne 
have the typical structure of the genus and extend nearly or quite to the fourth 
cephalothoracic segment. The structure of the swimming feet is typical. PI. I, 
fig. 10 shows the fourth foot. It is somewhat interesting that in the case of 
the individual from which this was drawn the companion fourth foot had five 
setze on the terminal segment of the endopodite instead of the regular number, 
six. The second segment of the fifth foot has a seta about midway of its outer 
margin. The third segment is about one and a half times as long as the first 
and bears a long spine at about midway of its outer border and another at its 
outer distal angle; the inner distal angle is prolonged into an unguiform process, 
‘which projects at an angle of forty-five degrees with the axis of the segment; 
the distal border of this process is armed with a variable number of teeth, as 
many as eleven having been counted. The fourth segment is one-half as long 
as the third and bears a spine at its inner distal angle and a long terminal spine. 
Pl. II, fig. 2 shows the fifth foot. 
Matr.—The form of the male cephalothorax is like that of the female, but 
is somewhat narrower and more elliptical than oval in outline. The cephalo- 
thoracic appendages, with the exception of the fifth feet, are those typical of 
the genus. The abdomen, Pl. II, fig. 4, is slender, the segments being about 
equal to each other in length. The furcal rami equal in length the three pre- 
ceding segments; the inner margin is ciliate and the outer very sparsely so; 
the hairs are much finer than those on the female furca and are comparatively 
few in number; the fifth foot is shown in Pl. II, fig. 7. The right foot is dis- 
tinctly four segmented. The left foot terminates in two finely ciliated prom- 
inences. 
Length, exclusive of furcal sete: males 1.95 to 2.1 mm., females 1.9 to 
2.25 mm. . 
It is very probable that some of the immature forms collected in other 
localities belong to this species. The single individual collected at Herschel 
island, however, was not £. canadensis, and does not correspond to any other 
described species. In the absence of more material it does not seem wise to 
attempt a description of it. 
Granting that the immature individuals were probably H. canadensis, it 
appears, from the fact that most of those collections were made earlier than this 
one of September 23, that this species matures in the late fall. 
Heterocope septentrionalis Juday and Muttkowski. 
Plate IT, figs. 3, 5, 6, 8-13. 
This species was described by Juday and Muttkowski in 1915, pp. 27-30, 
fig. 4, A, B, C, D, E, and F, fig. 5, A, B, and C, fig. 6, A and B, from material 
collected at St. Paul island, Alaska, and, as stated by them, undoubtedly differs 
from the species previously described. The forms collected by the Canadian 
Arctic Expedition differ only in certain minor details which should be considered 
as variations within species limits. The female abdomen is shown in Pl. I, 
fig. 3. The processes of the genital area of the first abdominal segment are 
described and figured by Juday and Muttkowski as “ trilobate.”” The specimens 
examined in these investigations have shown much variability in the form of 
these processes. They have been found trilobate as shown in PI. II, fig. 10, 
indistinctly trilobate as in Pl. II, fig. 11, and bilobate, as in Pl. II, fig. 12. In 
the fifth foot of the female shown in PI. II, fig. 5, the teeth of the inner margin 
of the terminal segment are distinctly serrate. 
The abdomen of the male is shown in Pl. II, fig. 6. The external spines of 
the right exopodite of the second foot are distorted, as in the figure of Juday and 
Muttkowski. This is shown in Pl. II, fig. 9. The spine of the first segment of 
the right exopodite is shown in Pl. II, fig. 13. The fifth feet of the male, shown 
49086—2 , 
