Cyclops kolensis in North America — Reed 
wider than the genital segment. The rami are 
about 6 times as long as wide. The inner ter- 
minal setae are a little longer than the rami and 
twice the length of the outer. The seminal 
receptacle is pictured as not filling as large a 
portion of the genital segment as it does in 
C. kolensis . 
DESCRIPTION OF THE ALASKAN SPECIMENS 
Female. The total length exclusive of the 
furcal setae is 1.2— 1.5 mm with most ranging 
from 1.3— 1.4 mm. 
The antennules of the St. Matthew Island 
specimens (about 15 were available for study) 
are either 16- or 17-segmented (Fig. 1). Con- 
siderable variation was observed in the number 
of segments of the antennules of about 15 Pt. 
Barrow animals: a few had 17 ; more frequently 
the number was either 12 or 11. Twelve-seg- 
mented antennules resulted from the incomplete 
separation of segments 12, 13, and 14, and 8, 
9, 10, and 11 (Fig. 2). The joint between 
segments 11 and 12 was distinct in all cases. 
Eleven-segmented antennules resulted from 
fusion of the segments as in the 12 -segmented 
antennules plus the failure of segments 3 and 4 
Figs. 1 and 2. Antennules of female Cyclops 
kolensis. 1, 16 segments, St. Matthew Island, Alaska; 
2, 12 segments, Pt. Barrow, Alaska. 
253 
to separate completely. Gurney (1933:48) in- 
dicates that in C. strenuus segment 3 of the 5 th 
copepodite antennule gives rise to segments 3 
and 4 of the adult, and he suggests further that 
segments 8, 9, 10, and 11 of the adult arise 
from segment 7 of the 5 th copepodite and like- 
wise segments 12, 13, and 14 of the adult 
derive from segment 8 of the copepodite. 
Gurney states (1933:59) that female Cyclops 
(species not indicated) possess a total of 43 
setae and three aesthetes on each antennule. The 
antennules of the Alaskan specimens, whether 
17- or 12- or 11 -segmented, bore this number 
of setae and aesthetes. 
The posterior corners of the 4th thoracic seg- 
ment were either smoothly rounded or, more 
frequently, produced into laterally directed small 
processes (Figs. 10 and 11) ; in no instances 
were the corners expanded into wing-like shapes. 
All animals examined possessed a spine formula 
of 2, 3, 3, 3 (Figs. 3-6). 
To facilitate description of individual vari- 
ability found in the Alaskan specimens and to 
aid in comparing them with forms of C. kolensis 
described in the literature, a series of animals 
from each locality was measured. Table 2 sum- 
marizes measurements of morphological features 
which have been used traditionally in working 
with C. kolensis. 
In this study of variability, ratios of body 
parts often have been found to be more useful 
than absolute measurements. Therefore Table 3 
was prepared. Because the ranges of ratios are 
based on means it 90 % confidence limits, the 
ranges have a confidence limit of 81 %. The 
effect of treating two St. Matthew Island collec- 
tions separately and combined is also indicated 
in Tables 2, 3, and 4. 
Clearly, the Pt. Barrow and St. Matthew 
Island populations are referable to C. kolensis 
as characterized by the morphological features 
used in Table 1. How similar to each other are 
the Alaskan populations? This question is im- 
portant in helping to understand the relation- 
ships of the North American forms to those 
reported from other regions. Figure 18 indi- 
cates that among the Alaskan animals those 
from Pt. Barrow tend to be larger than those 
from St. Matthew 809 which are, in turn, larger 
than St. Matthew 814 individuals. The excep- 
tions are lengths of inner spines of terminal 
