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PACIFIC SCIENCE, Vol. VIII, April, 1954 
Fig. 3. Acanthomysis borealis, n. sp. a. Anterior region, dorsal aspect; b, sixth thoracic leg; c, abdomen, lateral 
view; d, uropod (statocyst spines are on other side of inner uropod); e, telson; /, tip of telson, {a, b, d, e, scale 
A; c, scale B; /, scale C.) 
Island, Alaska, described by me as Acantho- 
mysis sp. in 1949 . (In the description of this 
species [p. 102] there is a typographical error: 
the telson is 1.7 mm. long instead of 0.7 mm. 
long.) There are slight differences in propor- 
tions as, for example, those of the eyes, 
squame, and telson; the dorsal papilla of the 
ocular peduncle was not observed previously; 
and there are .flight differences in the rugae 
and folds of the abdomen. But as the general 
configurations are similar and the distal end 
of the telsons are almost identical, and as the 
Kodiak specimen is markedly immature, the 
differences are not considered to be enough 
to warrant separation of the two forms. 
The Kodiak specimen was left unnamed, 
as it was felt that without mature specimens 
too much faith should not be placed in its 
characteristics. This specimen shows that the 
distinguishing characteristics, especially the 
telson, are not influenced by growth. It is 
unfortunate that there are no mature males 
available, but the unique telson should be 
adequate to separate this species from related 
species, whether male or female specimens 
are examined. 
As discussed under A. alaskensis, there are 
now seven species in the genus Acanthomysis 
with rugose abdomens. Some of the character- 
istics of those species are discussed under A. 
alaskensis; here it will suffice to say that all 
other members of the group have plainly 
truncate telsons with relatively straight sides 
immediately proximal to the truncation and 
that in all of them the posterolateral spines 
of the telson are markedly larger than the 
spines immediately adjacent on the lateral 
margins. In this species, on the other hand, 
the posterior margin of the telson is so in- 
decisively truncate that it appears rounded, 
and the posterolateral spines are only slightly 
larger than the adjacent spines. Other char- 
acteristics can be used to supplement these 
differences— the large medial spines found on 
the tip of the telson in A. sculpta, the dorso- 
ventrally compressed eye in A. alaskensis, etc. 
(see Table 1). 
Thysanoessa raschi (M. Sars) 
Thysanopoda raschii M. Sars, Vidensk. Selsk. 
Christiania, EorhandL, 1863, p. 83. 
