Mysidacea and Euphausiacea BANNER 
135 
With the geographic variation of Neomysis 
rayi and N. awatschensis, members of a closely 
related genus, in mind and viewing the rel- 
atively minor differences between the species 
of the Acanthomysis costata group, I am of the 
opinion that this complex, too, may represent 
only a single species with various geographic 
races. However, as I have been able to find 
no variation in those specimens that I have 
studied nor have variations been reported by 
workers from other of these species, and as the 
characteristics as they are now given are suf- 
ficient to separate the four forms, I have de- 
cided for the time to maintain them as four 
species. 
Acanthomysis borealis n. sp. 
Fig. 3 
Acanthomysis sp. Banner, Roy. Canad. Inst., 
Trans. 27: 101-102, pi. 6, figs. 17a-d, 1949. 
DESCRIPTION: Anterolateral corners of the 
carapace produced and acute. Rostrum tri- 
angular with acute tip reaching only to basal 
portion of ocular peduncle. 
Eyes similar to those of A. sculpta (Tatter- 
sall), 1.3 times as long as broad; corneas 
occupying distal 0.4, subhemispherical. Pe- 
duncle with very short dorsal papilla. 
Antennular peduncle 1.5 times length of 
eyes, slender, with first article slightly less 
than twice as long as broad. Basicerite of an- 
tenna with small but acute tooth; peduncle 
reaching only to end of first antennular article; 
squame 7 times as long as broad, with distal 
0.04 separated by usual articulation. 
Labrum with acute anterior process. Mouth- 
parts usual. 
Endopods of third to eighth thoracic legs 
with 5-7 secondary articulations in propodi; 
dactyli about 0.5 the diameter and length of 
distal propodal article. Basal plates of exopods 
with or without denticle. 
Abdomen with following grooves and folds : 
Segment 1 : single fold in middle; two rounded 
grooves ; 
Segment 2: single fold in middle; posterior 
groove poorly defined; 
Segment 3: same as segment 2; 
Segment 4: single fold in middle; posterior 
groove better defined; 
Segment 5: heavy rounded ridge in middle, 
discontinuous over midline and projecting 
on either side of midline as rounded lobes; 
posterior to middle ridge a heavy fold, 
almost discontinuous over midline; near 
posterior margin another rounded ridge and 
groove, also discontinuous; posterior mar- 
gin projecting over base of segment 6 as 
rounded lobe; 
Segment 6: similar to segment 5, except 
ridges and folds are heavier and discon- 
tinuous over midline, 
Telson 1.8 times length of sixth abdominal 
segment, 3.5 times as long as broad. Lateral 
margins anteriorly convex for short distance, 
then concave, convex again in middle, and 
in posterior half slightly concave. Tip so nar- 
rowly truncate and meeting rounded lateral 
margins at such an angle that it at first appears 
rounded. Spines of anterior half of lateral 
margins subequal in length; those from mid- 
dle to near tip alternating between longer 
spines and groups of 2-6 shorter spines; in 
posterior tenth spines again subequal in 
length and 0.5 to 0.66 length of long spines 
in preceding portion. Posterolateral spines of 
tip slightly longer than lateral spines adjacent; 
median terminal spines 0.5 length of postero- 
lateral spines. 
Inner uropod 0.7 length of outer, slightly 
shorter than telson and bearing four spines 
near statocyst. 
SPECIMENS examined: Type specimen: A 
mature female 19 tnm. long collected from 
the stomach of a cod by the U. S. Fish and 
Wildlife King Crab Investigation, No. C-108, 
off Port Moller, Bristol Bay, Alaska, in 20-22 
fathoms, May 6, 1941. U. S. National Mu- 
seum 95639. 
Paratype: an immature female, 15.5 mm. 
long, same data as type. 
DISCUSSION: These specimens agree well 
with the specimen from Olga Bay, Kodiak 
