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PACIFIC SCIENCE, Vol. XIV, April I960 
Fig. 3. Regression of the number of scale-rows on total body length of Auxis thynnoides. 
or less vertical direction, and the dark longi- 
tudinal band on the dorsal surface of the body 
does not taper noticeably until it reaches the 
end of the second dorsal fin, whence it continues 
to the base of the caudal fin, tapering very 
gradually. 
Another character often mentioned by in- 
vestigators in separating the two forms of Auxis 
is the difference in the roundness of the body. 
In both species the ratios of body length (fork 
length ) to body width are nearly identical ( 6.04 
to 6.56 in t hazard; 6.02 to 6.58 in thynnoides) ; 
however, the ratio of body length to body depth 
of thynnoides (4.55 to 4.98) is greater than that 
of thazard (4.32 to 4.56). Consequently, thyn- 
noides appears fusiform, whereas thazard, be- 
cause of its greater depth, appears laterally 
compressed. In visual comparison, this difference 
is so slight that it requires an unusually keen 
observer or one who has had practice in this ob- 
servation to notice the difference. 
Nearly all of the characters examined on the 
two species exhibit very small differences which 
are difficult to recognize in the field. Even the 
relatively more obvious corselet difference would 
elude detection unless the observer was looking 
for it specifically. This being the case, the ques- 
tion arises as to whether thynnoides was present 
in these waters previous to this capture but was 
undetected, or whether its recent capture in- 
dicates a movement of this fish into the area. 
REFERENCES 
Bleeker, Pieter. 1854. Faunae ichthyologicae 
japonicae species novae. Natuurk. Tijdschr. 
Ned.-Ind. 6: 395-426. 
1855. Vijfde bijdrage tot de kennis der 
