COLLETTE and CHAO: SYSTEMATICS AND MORPHOLOGY OF THE BONITOS (SARDINI) 



SPHENOTIC 

 PTEROSPHENOID 



LATERAL ETHMOID 

 VOMER 



PROOTIC 



PTEROTIC 



INTERCALAR 



FIRST VERTEBRA 



ETHMOID 



BASIOCCIPITAL 



FRONTAL 



PARASPHENOID EXOCCIPITAL 



BASISPHENOID 



Figure 19.-Ventral view of skull of Allothunnusfallai, California, 680 mm FL. 



slightly among the bonitos in shape. Cybiosarda, 

 Orcynopsis, and Gymnosarda have a beer bottle- 

 shaped window; it is roughtly triangular with a 

 broad arched posterior margin in Sarda. In 

 Allothunnus, a thin bony membrane is present 

 along the inner edge of the pterosphenoid toward 

 the center of the window. The pterosphenoids do 

 not fuse with the parasphenoid, as they frequently 

 do in large specimens of Thunnus thynnus (Gibbs 

 and Collette 1967). 



Lachrymal. -The lachrymal is an elongate bone 

 that covers up part of the maxilla and is attached 

 to the lateral ethmoid by means of a dorsal 

 projection on its inner surface (Figure 9). This 

 process is most pronounced in Gymnosarda and 

 most flattened in Allothunnus. The anterior mar- 

 gin of the lachrymal has an indentation with an 

 anteriorly projecting process on the dorsal margin 

 of the indentation (Figure 28). The margin is 

 slightly concave in Sarda and Gymnx)sarda com- 

 pared to the deep notch present in the other boni- 

 tos, Cybiosarda has the longest anterior process, 

 much longer and thinner than in Orcynopsis. 



Gymnosarda has a wide blunt process. The 

 lachrymal is relatively shorter and stronger in 

 Gymnosarda and it is extremely heavy and sculp- 

 tured at the dorsal projection and along the pos- 

 terodorsal margin. 



Suborbital bones.-Nakamura and Mori (1966) 

 stated that the first and second suborbital bones 

 are inconspicuously developed and not much 

 differentiated from the scales on the cheek in 

 Allothunnus. Suborbital bones are present in the 

 bonitos, but we have made no special effort to 

 study them. 



Sclerotic— The sclerotic bones consist of two 

 thickened semicircular segments connected by 

 cartilage on the inner lateral surface and by cor- 

 neal membranes on the outside. The inner rim of 

 the sclerotic bones appears elliptical externally in 

 all bonitos as in Thunnus atlanticus (de Sylva 

 1955, fig. 7). 



OTIC REGION.-This region encloses the otic 

 chamber inside the skull, and is formed by the 



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