Arctic Zooplankton — JOHNSON 
segment is slightly raised dorsally at the hind 
edge.) The fifth thoracic segment is extended 
into laterally projected "wings” that vary con- 
siderably in length and hyalinity. Many adult 
specimens were observed in which the left wing 
was only slightly developed, although the right 
wing was always well developed. The first an- 
tennae reach to, or slightly beyond, the fifth 
thoracic segment. The genital segment is nearly 
symmetrical and only slightly constricted lat- 
erally. It bears no lateral expansions but in lat- 
eral aspect has a rather conspicuous genital 
operculum. The anal segment is armed dorso- 
laterally with patches of fine spinules, best ob- 
served in aqueous media. (Sars states that in E. 
gracilis "the last caudal segment is perfectly 
smooth without any trace of the densely crowded 
spikes clothing the dorsal face of this segment 
in T. (E.) hirundoides .”) The caudal rami are 
provided with fine "hairs” on both their inner 
and outer margins. The longest caudal setae are 
only slightly longer than the rami. The terminal 
spine of the exopod of the second, third, and 
fourth swimming feet (Fig. 11) is cultriform 
as in E. gracilis. The fifth feet (Fig. 13) are 
symmetrical as in E. gracilis , and the first exopod 
segment bears a heavy, slightly setose, ungui- 
form process directed inward. There are two 
spines on the outer margin of this segment. The 
end segment is short and bears one long ter- 
minal spine and one short outer spine. The 
terminal spine of the exopod of the third and 
fourth feet is somewhat broadened in the mid- 
dle and is shorter than the end segment. In the 
male this spine is longer and more slender. The 
genital operculum is rounded (Fig. 16) in con- 
trast to the pointed operculum of the closely 
related species E. affinis as described and figured 
by Gurney (1931), and which he considers 
synonymous with E. hirundoides. 
MALE (Figs. 5-6): Length 1 .0-1.2 mm. The 
body is slender and nearly parallel-sided ante- 
riorly but tapers posteriorly. The body propor- 
tions are about as follows: metasome 57, uro- 
some (without caudal rami) 25, caudal rami 
15. As in the female, the anal segment bears 
dorsal patches of tiny spinules. The caudal rami 
have fine "hairs” on the inner and outer margins. 
The right geniculated first antenna has 25 seg- 
ments with moderately heavy spines on seg- 
319 
ments 8, 9, and 12. The fifth feet (Figs. 14, 
15) are asymmetrical, uniramous, and each 
exopod consists of two segments. The specific 
characters separating the species from closely 
related forms are seen mainly in the basal seg- 
ments and in the relative proportions of the 
segments of the rami. At the inner proximal 
margin of the second basipod of the right foot 
there is a well-defined rounded projection and 
associated smooth notchlike depression suggest- 
ing the specific name. The inner margin of the 
first basipod of the left foot projects down- 
ward, forming an irregular blunt process over- 
lapping about one-third the length of the sec- 
ond basipod. The second basipod is broadened 
with an inward expanse forming a dull flange 
along the long axis of the segment. Sars’ plate 
8, figure 16, shows no trace of these three fea- 
tures for E. gracilis. Otherwise the exopod seg- 
ments agree with that species which, however, 
appears to have a shorter first exopod segment 
on the left foot. The uncertain species described 
by Kiefer (193d) also differs in the absence of 
these characters and in the shape of the second 
basal segments of each foot. The second an- 
tennae and the mouth appendages of E. foveola 
are similar in the two sexes and appear to have 
no specific character except perhaps for the 
shape of the mandibular blade (Fig. 17). Few 
illustrations of other species are available with 
which to make comparisons, but the gap be- 
tween the first and second tooth is considerably 
wider than that figured by Gurney (1931) f° r 
E. affinis, Sars ( 1903 ) for E. velox, and Wilson 
(1953) for E. yukonensis and E. composita. 
It should be mentioned that a single damaged 
female specimen of a Eurytemora was collected 
by the Canadian Arctic Expedition offshore near 
Cape Thompson. Willey (1920) tentatively re- 
ferred it to E. gracilis. It is not possible to con- 
clude what species he dealt with but the prox- 
imity of the catch to the lagoons so richly pop- 
ulated by E. foveola makes it highly likely that 
it had been washed out from a nearby lagoon. 
Although there may be an intermittent present- 
day connection between the Yana River popula- 
tion and that in the Cape Thompson area, it 
must be a very tenuous one for a fresh- or brack- 
ish-water species, especially in view of the pre- 
vailing oceanic circulation northward through 
