FISHERY BULLETIN: VOL. 73, NO. 3 



SPHENOTIC 



PROOTIC 



PTEROTIC 



FRONTAL 



LATERAL ETHMOID 



VOMER 



INTERCALAR 



ETHMOID 



FIRST VERTEBRA 

 BASIOCCIPITAL 



EXOCCIPITAL 



PARASPHENOID 



PTEROSPHENOID 



BASISPHENOID 

 Figure 16.-Ventral view of skull of Orcynopsis unicolor, Tunisia, 543 mm FL. 



Frontal. -Most of the dorsal surface of the 

 cranium is covered by large concave frontal bones. 

 In dorsal view, the anterior ends of the frontals 

 overlap the posterior part of the ethmoid. 

 Posteriorly, they articulate with the sphenotic, 

 pterotic, parietal, and supraoccipital bones. The 

 frontal bones are thickened laterally to form the 

 roof of the orbit; they become thinner where they 

 meet along the median line of the skull and form a 

 crest. A thin bony inner lateral crest begins at the 

 middle of each frontal bone and continues along 

 the parietal to the epiotic bone. A pineal foramen 

 is present immediately anterior to the supraoc- 

 cipital crest. The pineal foramen is slitlike and 

 filled with cartilage in most bonitos. Allothunnus 

 has the largest and thickest frontal bones; they are 

 concave dorsally, with deep conspicuous radiating 



ridges and lack a frontal crest. A deep round 

 depression, lined with bony ridges, is present 

 anterior to the oval pineal foramen. This feature 

 of Allothunnus is similar to that in 

 Acanthocybium (Conrad 1938). Grammatorcynus 

 also has many conspicuous shallow radiating 

 ridges on the frontal bones. In ventral view, the 

 frontal bone articulates with the lateral ethmoid 

 anteriorly, the pterosphenoid medially, and the 

 sphenotic posteriorly. The ratio of the length of 

 the external edge of the frontal bone to the length 

 of the skull (anterior edge of the vomer to the 

 articulation of the first centrum) varies from 30.9 

 to 33.3% in S. australis (3 specimens 363-495 mm 

 FL) and thus differs from other species of Sarda, 

 whose ratios were less than 28%. Laterally, the 

 frontal bone divides into two shelves posteriorly 



542 



