70 PROCEEDINGS OF THE NATIONAL MUSEUM VOL. 125 
reduced. Female and male sternal furca (fig. 27/) well developed, 
Y-shaped, distal ends of rami rounded. 
Thoracic legs I-III biramous although endopodite of first leg 
rudimentary; fourth thoracic lez unirmaous, 3-segmented. For nature 
and armature of thoracic legs, see figures 28a—f and table 11. 
Discusston.—The diagnostic characteristic of Caligus alaihi is 
the combination of a 2-segmented abdomen on the male, denticulations 
on the second segment of the endopodite of the second thoracic leg 
(but not on the first segment), and the presence of only 1 plumose 
seta on the inner surface of the second segment of the exopodite of 
the first thoracic leg. Of these three, the most uncommonly found 
feature in other members of the genus is the presence of a single 
seta on the inner surface of the second segment of the exopodite of 
TABLE 11.—Armature of thoracic legs I-IV of the female and male of Caligus 
alaihi, new species 
Inter- Protopodite Exopodite Endopodite 
Leg | Surface podal SS oe SECON Raa 5 
Plate 
1 2 1 2 3 1 2 3 
I | Outer 8s, p rh 3H e 
Inner p c p 
II | Outer m,p m,mH | mH rh, mh,Q | ¢ D 3P 
m 
Inner Sie m,s Che cr B 5P 12 c,; 2P 3P 
ee NA Pe ls || are ee | ee ee | ed Ee eee | ee a 
III | Outer r,m,p ¢c, p’ Cy3p’, e c c, 3P 
m 
Inner 3s,P,m,s H CweE 3P 1? 3P 
IV | Outer 2s, p fm, mH | 4fm, 3mH, : | 
H 
the first thoracic leg. This feature, however, is found in at least one 
other species, Caligus pagrosomi Yamaguti, 1939. Caligus alaihi can 
be most readily distinguished from C. pagrosomi by the presence of 
denticulations on the second segment of the endopodite of the second 
thoracic leg, in contrast to the plumosities presumed to be found on 
the same segment of C. pagrosomi. (Yamaguti, 1939, does not provide 
a description of the second thoracic leg of C. pagrosomi but does indi- 
cate, p. 445, that the species is very similar to C. epinepheli Yamaguti, 
1936, which does possess plumosities on the second segment of the 
endopodite of the second thoracic leg.) Caligus alaihi can also be 
distinguished from C. pagrosomi by the apparent length of the abdo- 
men of the female, that of C. pagrosomi being approximately twice the 
length of that of C. alaiki. This characteristic, however, should be 
used with some reservation as the variability (or potential variation) 
