FISHERY BULLETIN: VOL. 73, NO. 3 



SPHENOTIC 



FRONTAL 



PTEROTIC 



INTERCALAR 



LATERAL ETHMOID 



ETHMOID 



FIRST VERTEBRA 



VOMER 



EXOCCIPITAL 



EPIOTIC 



PINEAL FORAMEN 



PARIETAL 



SUPRAOCCIPITAL 



Figure 14.— Dorsal view of skull of Orcynopsis unicolor, Tunisia, 543 mm FL. 



porting axis of the roof of the mouth. Ventrally, 

 the vomer of Cybiosarda and Orcynopsis (Figures 

 15, 16) has a blunt anterior edge and bears a patch 

 of villiform teeth. Sarda australis and S. sarda 

 frequently have a few small teeth on the middle of 

 the expanded part of the vomer, but vomerine 

 teeth are absent in the other bonitos. Some 

 specimens of S. chiliensis have a ridge along the 

 midline of the vomer but most have this area flat 

 or convex. The variation is individual, not 

 geographic: 3 of 12 southeastern specimens have a 

 ridge; 6 of 26 northeastern specimens have a ridge. 

 Godsil (1955) mentioned that the ventral surface 

 of the expanded portion of the vomer was flat in 

 Indo-West Pacific S. orientalis and that of eastern 

 Pacific specimens was slightly cupped or concave 

 ventrally. We found that this character is not con- 

 sistent in our material. The anterolateral edges of 

 the vomer are prominent and project ventrally in 

 Gymnosarda. The anterior one-third of the vomer 



in Allothunnus projects ventrally with an axelike 

 anterior end and is porous in the middle of the 

 ventral surface. The pointed posterior end of the 

 vomer is more elongate in Sarda than in other 

 genera of bonitos. 



The bonitos fall into three groups based on 

 vomerine dentition. Allothunnus, Sarda orien- 

 talis, and S. chiliensis lack vomerine teeth. A few 

 small teeth are frequently present on the head of 

 the vomer in S. sarda and S. australis and some- 

 times in Gymnosarda. Both Orcynopsis and Cybio- 

 sarda have a small patch of teeth on the head of 

 the vomer and a few teeth usually extend pos- 

 teriorly a short distance on the shaft of the vomer. 



Nasal. -The anterior end of the nasal, which 

 reaches the premaxilla posterodorsally, is 

 thickened in all bonitos and has an expanded 

 hammerlike head except in the species of Sarda 

 (Figure 27). The nasal gradually becomes thinner 



540 



