Juvenile Tunas— SCHAEFER and MARR 
265 
fish increase in size the gill rakers not only in¬ 
crease rapidly in length, but their number ap¬ 
parently increases. Counts of rakers on the first 
arch on specimens of various sizes are as fol¬ 
lows: 
48 mm. 8 + 25 
52 mm. 9 + 25 
61 mm. 10 + 26 
86 mm. 11 + 27 
The vertebrae, counting the urostyle, are 
19 + 18 in one stained specimen and 20 + 17 
in the other. They bear large inferior foramina 
on the last three or four precaudal vertebrae 
and on the first nine or ten caudal vertebrae. 
The haemal canal is very large, being broader 
than the body of the vertebrae beneath the 
precaudal and anterior caudal vertebrae. The 
lateral processes of the posterior caudal ver¬ 
tebrae are well developed in both specimens; 
there are no lateral processes on the anterior 
precaudal vertebrae. The first complete haemal 
arch was found to be on the 15 th vertebra by 
dissection of the 56 mm. specimen. 
Specimens of all sizes in our collection have 
about 20 to 30 conical, inwardly curved teeth 
on each side of each jaw. The palatines each 
bear a row of eight to ten rather large conical 
teeth. The vomer bears four or five rather 
small teeth which may be easily overlooked. 
Our very smallest specimens, of about 30 
mm., have visible the remnants of three spines 
at the lower posterior angle of the preopercle. 
In larger specimens the growth of the bone 
has completely obliterated these. Smaller speci¬ 
mens than those in our collection may be pre¬ 
sumed, by analogy with Neothunnus, to have 
more prominent and perhaps more numerous 
preopercular spines. 
The intestine of these specimens, as is char¬ 
acteristic of the Katsuwonidae, is relatively 
straight and is not folded. It runs back along 
the right inferior portion of the stomach. The 
liver is in three lobes, the right lobe being very 
much longer than the other two. In seven 
specimens examined, the right lobe of the liver 
extended posteriorly three-fourths or more of 
the length of the body cavity. 
That these specimens belong to either the 
genus Euthynnus or Katsmuonus is indicated 
by the morphology of the vertebral column. 
The well-developed inferior foramina on some 
precaudal as well as caudal vertebrae, forming 
with the very large haemal arches the so-called 
"trellis,” is characteristic of these genera (Starks, 
1910; Kishinouye, 1923). 
These specimens have several characters 
agreeing with Euthynnus but not Katsmuonus . 
The very great elongation of the right lobe of 
the liver is definitive. In Katsuwonus, both in 
adults described by Kishinouye (1923: 363, 
450, and 453, Fig. N) and by Godsil and 
Byers (1944: 11, 30), and in juveniles described 
by Schaefer and Marr (in press), the right 
lobe, although much larger than the other two, 
is not nearly as large as that of these specimens, 
which corresponds to Kishinouye’s description 
of the liver of Euthynnus. The first closed 
haemal arch of Katsuwonus occurs on the 12th 
vertebra according to both Kishinouye and 
Godsil and Byers, whereas Kishinouye states 
that Euthynnus has the first complete haemal 
arch further back, on the 16th vertebra. The 
low vertebral count of our specimens is also 
definitive, although this was a matter of some 
concern at first because it does not agree with 
the literature. Kishinouye (1923: 338, 452) 
found that Euthynnus has 39 vertebrae count¬ 
ing the urostyle, probably based on E. yaito 
alone. He described E. lineatus from a single 
specimen from Manzanillo, Mexico, but prob¬ 
ably did not dissect the fish to count the verte¬ 
brae. (Kishinouye: in the Suisan Gakkwai Ho, 
III, 113, 1920. We have been unable to 
examine this reference and our information is 
from Kishinouye, 1923.) He differentiates this 
species from E. yaito on the coloration and the 
relative size of the head. In his discussions he 
assumes all species of Euthynnus to have 39 
vertebrae. This matter was cleared up through 
the kind cooperation of C. R. Clothier of the 
