FISHERY BULLETIN: VOL. 73, NO. 3 



and the seven branchiostegal rays), and tvi^o 

 median unpaired bones, the glossohyal and 

 urohyal. 



Hyomandibula.-The hyomandibula is an in- 

 verted L-shaped bone that connects the man- 

 dibular suspensorium and opercular bones to the 

 neurocranium (Figure 9). Dorsally, there are three 

 prominent condyles. The longest and anteriormost 

 forms the base of the L and fits into the fossa at 

 the junction of the pterotic and sphenotic bones. 

 The dorsal condyle articulates with the ventral 

 fossa of the pterotic and the lateral process is at- 

 tached to the inside of the opercle. Anterolaterally 

 the hyomandibula joins the metapterygoid; 

 posterolaterally it has a long articulation with the 

 preopercle. 



Godsil (1954, 1955) found two differences 

 between the hyomandibula in Sarda orientalis 

 and S. chiliensis. In both species a spine protrudes 

 posteriorly from the center condyle. The spine 

 forms an angle of 90° or less with the major axis of 

 the hyomandibula in S. orientalis and greater than 

 90° in S. chiliensis. We confirm this difference and 

 use the character to divide the bonitos into groups. 

 Sarda chiliensis, Cybiosarda (Figure 39a), and 

 Orcynopsis (Figure 39b) have the angle greater 

 than 90°; Gymnosarda and Allothunnus probably 

 belong in this group based on the angle, but the 

 spines are greatly reduced in both genera. Sarda 

 orientalis has the angle 90° or less. Sarda sarda 

 (Figure 39c) and S. australis are intermediate 

 between the two groups in having the angle about 

 90°. 



Godsil used the length of the spine on the ridge 

 of bone next to the groove into which the 

 preopercle fits as a second character to distinguish 

 S. orientalis from S. chiliensis. The spine is much 

 longer in S. orientalis and projects beyond the 

 center condyle when the spine is placed flat with 

 the internal side down. Again we can confirm this 

 difference and note that S. sarda agrees with 

 Godsil's description of S. orientalis. Sarda aus- 

 tralis and S. chiliensis have the spine short and 

 not protruding. Godsil (1955:34) noted that on one 



Figure 39.-Right hyomandibulae of six species of Sardini, ex- 

 ternal view. a. Cybiosarda elegans, New South Wales, 365 mm 

 FL. b. Orcynopsis unicolor, Tunisia, 645 mm FL. c. Sarda sarda, 

 Tunisia, 504 mm FL. d. Sarda australis, New South Wales, 495 

 mm FL. e. Gymnosarda unicolor, Amirante Islands, 713 mm 

 FL. f. Allothunnus fcdlai, Tasmania, 778 mm FL. a and c drawn 

 twice as large as e and f, b and d drawn L5 times as large. 





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