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PACIFIC SCIENCE, Vol. XV, July 1961 
Fig. 2. Length frequency histogram for Limnocalanus johanseni adult (copepodid VI) population. 
Limnocalanus grimaldi (de Guerne) 
A total of 25 specimens was taken in lagoon 
no. 1 north, mostly near the bottom at a depth 
of only 3 m. Specimens were compared directly 
with L. grimaldi taken in 1950 in the Beaufort 
Sea at various stations offshore near Collinson 
Point and the Colville River. The fresh-water 
species L. macrurus Sars has not been seen for 
comparison. The Beaufort Sea specimens which 
were re-examined at this time agree well with 
the descriptions given in the literature for L. 
grimaldi . The head is not in the least vaulted 
as occurs in various degrees in L. macrurus , and 
there is only a slight cervical depression (Sars, 
1897: pi. 4, figs. 2, 3, 17). The structure of the 
fifth feet also agrees. The first antennae of the 
female reach beyond the anterior margin of 
the anal segment. In the male there are five 
distinct segments in the distal end of the right 
antenna beyond the geniculation. The deviations 
from descriptions of grimaldi are mainly in the 
posterior margins of the fifth thoracic segment. 
These were smoothly rounded in some cases, 
but many specimens had the characteristic tri- 
angular or spine-like point, and this was some- 
times present only on one side. The caudal rami 
were about eight times as long as broad and 
were slightly longer in relation to the urosome 
than given by Sars. 
The specimens collected in lagoon no. 1 
north are here also considered to be L. grimaldi , 
since they agree in nearly all respects with the 
Beaufort Sea material. The posterior margin of 
the fifth thoracic segment was acutely pointed 
in most specimens, but a few occurred with 
smoothly rounded margins (a characteristic of 
L. macrurus ) ; there were, however, only four 
distinct segments in the distal end of the male 
right antenna beyond the geniculation. This is 
also a characteristic of L. macrurus , although 
Marsh (1933) states that in exceptional cases 
there may be five segments. The lagoon speci- 
mens were slightly smaller than those from the 
Beaufort Sea, namely 2.6 to 2.7 mm. as opposed 
to 2.9 to 3.3 mm. for females. 
Since the condition of the fifth thoracic seg- 
ment is obviously an unreliable character, one 
is left to choose between the relative specific 
value of the outline of the head, and the seg- 
mentation of the distal end of the male first 
antennae. Both of these are variable for L. 
macrurus . The habitat presented by lagoon no. 
1 north is probably an important consideration, 
for although it was virtually fresh at the time 
and place of sampling, it is shallow and so near 
the sea that it may be reached by very high 
storm waves. This environmental situation may 
constitute an interesting natural experiment in 
which a landlocked population of L. grimaldi 
