Mysidacea and Euphausiacea ■ — BANNER 
SPECIMENS examined: Naknek River, Alas- 
kan Peninsula (Bristol Bay, approximately 
59°N., 157°W.)5 low tide, near shore, July 
11, 1946; Chester R. Mattson, collector; spec- 
imens loaned by Dr. J. E. Lynch, University 
of Washington. About 50 specimens. 
DISCUSSION: The animals of this complex, 
described as five different species and more 
recently resolved to three species (N. awat~ 
schensis, N. intermedia, and N. mercedis), are 
known to extend around the rim of the North 
Pacific from San Francisco, California, to the 
coasts of Japan and China. N. mercedis reached 
from San Francisco Bay to the waters of 
southern British Columbia; N. intermedia from 
south central Alaska and Bering Island to the 
coasts of Siberia, Japan, and China; and N. 
awatschensis was known only from Kamchatka 
(Tattersall, 1951: 190, in his distributional 
lists forgot to mention the type locality, 
Awatscha Bay in Kamchatka), Japan, and 
China. All are known to inhabit brackish 
water, and in Washington, at least, N. mer- 
cedis penetrates into fresh -water lakes (Banner, 
1948 A 75). 
These three forms, accepted as separate spe- 
cies, have been known to be closely related. 
Tattersall in 1932 (p. 321) and again in 1951 
(p. 187 et seq.) remarks upon this but gives 
criteria by which the species may be separated. 
The specimens listed above from the Bering 
Sea were somewhat intermediate in some of 
these criteria and have caused me to consider 
again, on the basis of the variations observed 
in specimens from Washington and Alaska, 
the validity of the separation of the three 
species. 
TattersalPs criteria for the separation of the 
three species are listed below, together with 
notes on the specimens from Washington and 
Alaska. 
Size: Tattersall states that mature N. awat- 
schensis are 10 millimeters long, whereas N. 
mercedis are 15 millimeters long. However, 
some mature specimens from Washington 
known as iV. mercedis are 11 millimeters long. 
The size of N. intermedia was not given by 
129 
Tattersall, but specimens from Alaska ap- 
proaching that species are 10 millimeters long 
and mature. 
Color: Tattersall states that N. awatschensis 
is black and N. mercedis ”is certainly not 
black.” Observations on living specimens 
originally identified as N. mercedis, both those 
collected so recently as to have the color un- 
changed and those kept alive in aquaria, have 
not shown any jet-black individuals, but the 
color was found to range from almost trans- 
parent to a condition where the chromato- 
phores were sufficiently expanded to make the 
individual almost black. In aquaria it was 
found that the color of the individuals changed 
with their environment. Several specimens 
were found that were pale green in color. 
This variability in the color pattern was rem- 
iniscent of Acanthomysis sculpta (Tattersall), 
which was found to vary from transparent, 
through sandy (and green), to jet black. To 
my knowledge there are no color notes on 
N. intermedia. 
Rostral plate: N. mercedis is supposed to have 
a quadrangular rostral plate, N. intermedia a 
rounded rostral plate, and N. awatschensis a 
pointed rostral plate. The forms from Wash- 
ington and from Alaska show variation in this 
plate, with only a few showing even an ap- 
proximation of the quadrilateral condition 
and the rest varying from broadly rounded 
to narrowly rounded. In none was the rostrum 
pointed; however, those in which the tip was 
narrowly rounded certainly approached the 
pointed condition. 
Antennal squame: This is supposed to be 8 
times as long as broad in N. mercedis and N. 
awatschensis but 10 times as long as broad in 
N. intermedia. In some of the specimens from 
Washington the squames are slightly longer 
than 8 times as long as broad, while in many 
of the specimens . from Bristol Bay the squames 
are about 9 times as long as broad. 
Eyes: In N. mercedis and N. intermedia the 
entire eyestalk is 1.5 times as long as the 
cornea is broad, with the cornea occupying 
less than 0.5 the length of the entire stalk 
