POST LARVAL TUNA FROM CEXTRAL AMERICA 



125 



table 2. The most anterior arch on both right and 

 left sides was counted. Specimens No. 7 and No. 

 8 are apparently too small to have a complete set. 



Table 2. — Oill-raker coui>ts ' of postlarval and juvenile 

 Auxis thazard 



' The method used in counting and recording gill rakers is the same as that 

 used by Wade (1949) in his discussion of the genus Auxis. 



The smallest Auxis in the collections is a dam- 

 aged 10-nim. specimen. Dermal pigmentation is 

 confined to narrow strips along the bases of the 

 second dorsal and anal fins and the dorsal and anal 

 finlets, along the lateral line from a point below 

 the posterior end of the second dorsal fin to the 

 posterior extent of the finlets, along the postero- 

 ventral margin of the orbit and to a small spot on 

 the point of the isthmus. The fins are usually 

 colorless although the first dorsal may bear a few 

 scattered melanophores. Four small spines occiu- 

 along the angle of the preoperculum. Each half 

 of the upper and lower jaws bears about 10 small 

 teeth. With increasing size of fish, the local centers 

 of pigmentation expand. On fish of 13 mm. the 

 dorsal strip of body pigmentation extends from the 

 operculum to the caudal at its point of least depth, 

 and a light coloration appears on the snout and 

 operculum. All areas in the dorsal hall" of the body 



of fish larger than 20 mm. bear at least a light 

 covering of pigment spots. The degree of pig- 

 mentation varies greatly from specimen to speci- 

 men in this species. The pattern here described is 

 that found to be the most common. 



EUTHYNNUS LINEATUS Kishinouye 



This species is represented in the collections by 

 27 specimens, ranging from 7.5 imn. to 23.5 mm. 

 in length. Two fish were cleared and stained 

 and each was found to have a vertebral count of 

 37, the first caudal vertebra in each case being 

 the twenty-fii'st. As is the case with Neothunnus 

 macrophrus and Auxis thazard, the viscera of the 

 smallest specimens cannot be studied adequately 

 unless specimens are sectioned. Schaefer and 

 Marr (1948a, 1948b) describe the viscera in speci- 

 mens of Euthynnus lineatus more than 15 mm. 

 long. The first dorsal, point of the isthmus, 

 anterior half of the lower jaw, tip of the snout, 

 posteroventral margin of the orbit, and operculum 

 of the smallest specimen (7.5 mm.) bear scattered 

 melanophores. Subcutaneous pigmentation cov- 

 ers the brain and the dorsal margin of the peri- 

 toneum. The only dermal pigmentation evident 

 on the body of this specimen is a pau- of light 

 spots at the posterior end of the anal fin insertion. 

 At 10.5 mm. in length, light pigmentation appears 

 at the base of the first and second dorsals. Body 

 pigmentation is still confined to the bases of the 

 anal and the two dorsal fins. By 14 mm., the 

 pigment has spread anteriorly from the base of 

 the first dorsal to the area overlying the brain. 

 Coloration along the lateral line first appears m a 

 16-mm. specimen as a few faint spots. On this fish 



Figure 4. — Eutlii/iniii.'! lineatus, 14 millimeters long. 



