myotomes is about thirty-eight, all of which characteristics set it apart from thorn. 

 The tip of the upper jaw is slightly blackish, there is one melanophore on the 

 metencephalon, and the spine at the angle of the preopercle' is very long. This 

 specimen is tentatively assigned to the genus Auxls since it resembles a larval fish 

 which was recorded by Ehrenbaum as a presumed larval form of this genus. There is 

 also a possibility that it may be a larval Euthynnus y&ito . 



Thunnidae 



A specimen, the generic and specific identification of which is as yet not 

 clear but which appears to be at any rate a larval form of one of the Thunnidae, was 

 taken in a plankton net while anchored off Takarajima on May 29, 1924.. The speci- 

 men, which was badly damaged, was about 6 mm long. 



Its characteristics are 18+21 vertebrae, a large head, mouth, and eye, black 

 walls to its body cavity, and an anus opening slightly anterior to the middle of 

 the body. The head is about half as long as the body, and the breadth of the head 

 is nearly twice that of the body at the point where the anus is located. The 

 preopercle has three spines on its lower edge, one long spine at the angle, at 

 least one spine on the posterior edge, and three small spines on its surface. The 

 upper and lower jaws have fifteen or sixteen teeth each and there are at least two 

 on the palatine. Melanophores in the cranial and body cavities are not as numerous 

 as in the presumed larval skipjack specimens, and, except as noted above, there is 

 hardly any other coloration visible. The dorsal fin is not high and the first and 

 second dorsals are not yet clearly separated. The rays of the second dorsal and the 

 anal are not yet well developed. 



Two postlarval tuna specimens were recovered from the stomach of a skipjack 

 taken on pole and line at Rakasone [_2B°10^ t 129°15'E]on May 16, 1924. (Figure 6). 

 They are about 34 mm in total length, the body is broad, the head is over half as 

 long as the body without the caudal fin, and the snout is slender and sharp so that 

 at first glance one might think them the larval form3 of spearfish or cybiids. The 

 first dorsal is high, the second dorsal and anal are low, and the pectoral, ventral, 

 and caudal fins are well developed. There are long spines on the preopercle, three 

 on the ventral edge, one at the angle, three on the posterior edge, and two on the 

 surface. The spine near the anterior extremity of the ventral edge points forward 

 so that it is roughly at right angles to the spine next to it. There are ten gill- 

 rakers on the ceratobranchial of the first gill arch, but only one is Just begin- 

 ning to appear on the epibranchial. There are 18 vertebrae anterior to the anus and 

 21 posterior to it. The first vertebra is notably lower than the second and succeed- 

 ing vertebrae. The epiphyses of the anterior vertebrae are broad, just as in the 

 mature fish and the lateral projections of the caudal vertebrae are somewhat devel- 

 oped. The teeth are of various sizes with about forty in the upper jaw and slightly 

 less than thirty in the lower jaw. There are eight teeth on the palatine, and none 

 are yet visible on the vomer and mesopterygoid. The teeth are well developed on 

 both the upper and lower pharyngeal bones. The basibranchials are just like those 

 of the mature fish. The posterior half of the postclavicle in these larval speci- 

 mens differs greatly from that of mature thunnids in being altogether flat and 

 straight with the anterior lamellate portion forming a long narrow triangle. The 

 posterior needle-shaped portion is about three times as long as the lamellate part . 

 and is roughly uniformly slender throughout its length. The pyloric caeca are pretty 

 well developed, but are shorter than those of the adult fish. The intestine has 

 the bend peculiar to the tunas, and although there are almost no longitudinal folds 

 in the walls of the rectum, they can be seen in other parts of the intestine. The 

 anus opens far posterior to the middle of the body. The gall bladder and the 

 spleen cannot be seen. There is black coloration on the surface of the body, 



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