268 
PACIFIC SCIENCE, Vol. II, October, 1948 
FIG. 4. Juvenile Auxis thazard photographed against a white background, illustrating lack of pigmentation of 
fins. 
extends to a point between the anterior margin 
of the iris and the vertical bisector of the iris, 
whereas in Euthynnus it generally extends to a 
point between the vertical bisector of the iris 
and the posterior margin of the iris. In the 
smaller specimens the lower jaw is shorter than 
the upper, but the jaws become equal at about 
50 mm. total length. The smallest specimens 
have three spines at the angle of the preopercle, 
but these are gradually grown over and dis¬ 
appear at about 35 to 40 mm. total length. 
There are indications, on alizarin-stained speci¬ 
mens, that seven more spines are present in 
smaller individuals. Similarly, a figure of a 17.5 
mm. specimen of A. thazard from the Medi¬ 
terranean (deBuen, 1932: Fig. 27) shows a 
total of nine preopercular spines. The lateral 
keel along the caudal peduncle starts to develop 
at about 40 mm. total length. 
The large dorsal interspace characteristic of 
Auxis actually contains small spines or rays. 
These are usually subcutaneous. Even in our 
smallest specimens they are not visible unless 
the fish is cleared and stained or unless the 
