Arctic Zooplankton — Johnson 
317 
has assumed some characteristics of its fresh- 
water counterpart, particularly in the fusion of 
two of the segments in the distal portion of 
the male right antenna. 
Limnocalanus johanseni Marsh 
A comparison of specimens of this species 
from the lagoons and from collections I made 
in Imikpuk Lake in 1957 shows only small 
variations in structure. Mention should be made, 
however, of some features that are not included 
in the original description. It was noted that 
in many specimens the fifth thoracic segment 
may be smoothly rounded or with only slightly 
angular outline. Marsh states that this segment 
is rounded on the sides, and each side is armed 
with a small spine which may be either sharp 
or blunt. Apparently inadvertently omitted from 
Marsh’s drawings is a long, heavy seta that oc- 
curs on the inner anterior distal angle of the 
second basis of the first feet. 
Centropages abdominalis Sato 1913 
Centropages mcmurrichi Willey 1920 
Willey (1920) was apparently unaware of 
Sato’s (1913) publication, and described this 
species as new under the name C. mcmurrichi 
n. sp. His description is without figures, but he 
considered the species to be identical with a 
copepod reported and figured by McMurrich 
(1916), with some reservations, as C. hamatus 
Lilljeborg. Examination of Alaskan material and 
reference to McMurrich’s figures, and to those 
of Sato ( photostatic copies of which are at hand 
through the courtesy of Dr. Takasi Tokioka and 
Isamu Yamazi of the Seto Marine Biological 
Laboratory), and of Mori (1937) leaves little 
doubt that these species are identical. 
Eurytemora pacifica Sato 1913 
Eurytemora johanseni Willey 1920 
This is a clearly defined species, principally 
on the basis of the fifth feet in the female (Figs. 
7-10). In the female, the fifth thoracic segment 
is provided with broad triangular wings, but 
breeding females were also found with this 
segment smoothly rounded (Fig. 8). The hya- 
line wing apparently may be shed or fails to 
develop. In the present study both males and 
females were found in the same catches. Willey 
(1920) described the species under the name 
E. johanseni n. sp. Sato described only the adult 
male, but his figures agree especially with 
Willey’s figures 11 and 12 of the fifth feet. 
Smirnov (1931) first pointed out the probable 
identity of the species. 
Eurytemora foveola n. sp. 
TYPES: Holotype, male, U. S. National Mu- 
seum no. 105996; allotype, female, USNM no. 
105997. Type locality, lagoon no. 6 south. 
In lagoon no. 6 south and nos. 1 and 2 north 
the dominant copepod was this hitherto un- 
known species. It was present in these lagoons 
in vast numbers and despite its small size con- 
stituted 90 per cent or more of the biomass in 
the samples from lagoon no. 6 south and no. 1 
north where it was actively reproducing and 
many females were found carrying eggs and 
spermatophores. In lagoon no. 2 north it was 
greatly surpassed in mass by the larger clado- 
ceran Daphnia. It is closely allied to Eurytemora 
gracilis, both sexes of which were described by 
Sars (1898) from the lower Yana (Jana) River 
and, judging from Sars’ figures and description, 
the females may be nearly indistinguishable. 
The chief differences separating the present 
species from that of Sars’ are structural details 
in the fifth feet of the males. In view of these 
small but apparently persistent differences, as 
shown by examination of a great many speci- 
mens, it seems best to designate it a new species 
rather than a variety of E. gracilis. 
FEMALE (Figs. 3,4): Length 1.15-1.25 mm. 
The body is slender in both dorsal and lateral 
aspects with about the following linear propor- 
tions: metasome (anterior division) 67, genital 
segment 11, first abdominal segment 6, anal 
segment 11, caudal rami 17. The metasome is 
slightly widest in the region of the first pe- 
digerous segment. There is a slight cephalic de- 
pression, but no medial knob on the postero- 
dorsal margin of the cephalic segment. (In E. 
gracilis the greatest width appears to extend 
somewhat farther forward according to Sars’ 
pi. 8, fig. 8; and in his fig. 9, the lateral profile 
also differs in that his species is relatively 
thicker through the midbody and the cephalic 
