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



depression continues from the interspace of the 

 posterior frontal shelves and separates the ptero- 

 tic from the sphenotic. In bonitos, the size of both 

 fossae varies only slightly; they tend to be deeper 

 and larger in Gymnosarda and Allothunnus. 



Prootic.-In ventral view, the prootic connects 

 with all ventral bones which compose the posterior 

 part of the neurocranium (Figures 15-19). The 

 prootic bones are irregular in shape and meet each 

 other along the ventral median line of the brain 

 case to form the anterior portion of the posterior 

 myodome. A prootic foramen is present 

 anterolaterally between the tip of the 

 parasphenoid wing and the sphenotic. The strut 

 forming the outer part of the foramen is absent in 

 Allothunnus forming a deep groove. The prootic 

 pit of the more advanced scombrids (Gibbs and 

 Collette 1967) is present in Allothunnus and ab- 

 sent or incipient in the other bonitos. In addition 

 to the distinct prootic pit in Allothunnus, there is a 

 very peculiar thick bony wing which is developed 



laterally; this twisted wing has a smooth convex 

 anterior surface and a concave posterior surface. 



Sphenotic. -The sphenotic bone forms the most 

 posterior dorsolateral part of the roof of the orbit. 

 It forms a continuation of the outer lateral shelf 

 from the frontal bones and articulates with the 

 pterosphenoid medially and the prootic and ptero- 

 tic posteriorly. The lateral process of the sphenotic 

 serves as an attachment for the outer process of 

 the supratemporal. This process is pointed in 

 Cybiosarda, Orcynopsis, Gymnosarda, and 

 Allothunnus, and is less sharp in the species of 

 Sarda. There are differences in the outlines of the 

 joints around the sphenotic bone with the adjacent 

 bones, but these are probably individual varia- 

 tions. 



Intercalar.-The intercalar (opisthotic) bone fits 

 between the pterotic and exoccipital bones 

 (Figures 10-14) and bears a dorsal protuberance 

 which connects to the lateral process of the post- 



SUPRAOCCIPITAL CREST 



EPIOTIC 



SPHENOTIC 



PARIETAL 



PTEROSPHENOID 



FRONTAL 



ETHMOID 



PTEROTIC 



INTERCALAR 



EXOCCIPITAL 



VOMER 



LATERAL ETHMOID 



PARASPHENOID 



FIRST VERTEBRA 

 BASIOCCIPITAL 



PROOTIC 



BASISPHENOID 

 FiGUKE 21.-Lateral view of skull of Orcynopsis unicolor, Tunisia, 543 mm FL. 



547 



