





5 ey 
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26 G Canadian Aretic Expedition, 1913-1918 — 

mandibular palp is thrown off, and the use of the second pair of antenn 
swimming instrument is discarded. Apparently both sexes occur there in equ: 
numbers, the males attaining the largest size. As the summer passes their 
numbers decrease, and their size seems to depend upon the length of time the ~ 
ponds they occur in carry any water. B 
I have examined a great number of specimens of this species from Green- 
land and arctic Eurasia, found in the museums in London and Scandinavia. 
Genus ARTEMIOPSIS Sars. 
Artemiopsis stefanssoni. 
Artemiopsis Stefanssont Jonansen, (Preliminary diagnosis in Canadian Freld- 
Naturalist, vol. xxxv, No. 2, p. 29, issued June 22, 1921). 
This species was secured in one of the three large tundra ponds situated at 
about 100 feet elevation on one of the gravel ridges near the coast of Bernard 
harbour, south of our winter house. I collected a number of mature males and 
females here, on October 6, 1915, by cutting a hole in the ice of the pond. 
IMMATURE STaGES 
On July 3, 1916,I secured, in the same pond, fourteen larvae presumably of 
the same species, measuring from two to three mm. in length. They were in the 
metanauplius and post-mentanauplius stage, the youngest of them having large 
second pair of antennae, and the abdomen (tail) not fully developed, though 
both the paired eyes, and 10 to 11 pairs of foliaceous legs were present. In the 
largest specimens the second pair of antennae were comparatively shorter, 
and all the nine joints of the tail (abdomen) to be seen. As even the mature 
specimens of the genus can hardly be distinguished from the genus Branchinecta, 
except in the sexual characters, it follows, that the larvae are practically of the 
same appearance as B. paludosa of corresponding age, so I do not find it necessary 
to figure them. From B. paludosa of the same size they are distinguished by 
having more of the adult characters (foliaceous legs developed, second pair of 
antennae shorter, etc.). The tail (abdomen) even when it has all its nine segments, 
is shorter and more solid-clumsy than tapering, with the cercopods (each of 
which ends in a long spine) less differentiated, as described under the adults. 
They were found in numbers among the stones covered: by detritus-mud 
and vegetation in the shallow bights of the pond, showing up by their pink or 
pale rose colour. They were rather sluggish in behaviour and fairly easy to catch 
by stirring up the water, which later that day (3.30 p.m.) had a temperature of 
55° F. (Air 50° F., clear and warm). ! 
Branchinecta paludosa was not observed in these three ponds (though both 
Lepidurus arcticus and other Entomostraca were common there (see p. 8), 
during our stay at Bernard harbour. At this time of the year B. paludosa at 
this locality had already reached such a size (1-14 cm.) that the two sexes could 
be easily separated, thus five times the length of the Artemiopsis larvae. When 
it is further remembered (see above and below), that the full grown Artemiopsis 
were secured the preceding fall in this same pond, there can be little doubt but 
that these larvae belong to the genus Artemiopsis, and not to Branchinecta. 
DESCRIPTION OF ADULTS 
I give some illustrations (text figures 5-6) of the adults of this new and 
interesting species, which shows certain differences from the only other species 
hitherto known, A. bungei Sars, from eastern Siberia, sufficiently characteristic 
to support a new specific name. The males (text-figure 5) measured from 7 
to 10 mm., and in spite of their small size they were fully mature, and continually - 
copulating with the females. They had the eleven pairs of foliaceous legs, and 
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