FISHERY BULLETIN: VOL. 82, NO. 4 



ly between the tip of the parasphenoid wing and 

 the sphenotic. There is no trace of the prootic pit 

 characteristic of the Thunnini and Allothunnus 

 (Gibbs and Collette 1967; Collette and Chao 1975). 

 Specimens differ in the number and arrangement 

 of foramina leading into the brain cavity from 

 inside the anterior opening of the trigemino- 

 facialis chamber, but these do not seem to be 

 useful interspecific differences. 



Pterotics. — The pterotics form the lateral pos- 

 terior corners of the neurocranium. Posteriorly, 

 each pterotic is produced into a truncate process 

 or pointed spine. The pterotics articulate with the 

 epiotics and parietals medially and with the 

 exoccipitals and intercalars posteriorly. A ridge, 

 the pterotic ridge, originates on the dorsal sur- 

 face of the posterior third of the frontal and 

 continues posteriorly, diverging to the posterior 

 corner of the pterotic, just anterior to the pterotic 

 spine. In ventral view, the pterotics articulate 

 with the sphenotics anteriorly and the prootics 

 and intercalars medially. Two contiguous fossae, 

 one at the posterior half of the pterotic bone and 

 one at its joint with the sphenotic, seat the dor- 

 sal and anterior condyles of the hyomandibula. 

 Three closely situated lateral sensory canal pores 

 open on each pterotic at the posteriormost region 

 of the pterotic crest. The largest pore is the most 

 posterior and opens dorsally; lateral to this is the 

 next largest opening laterally on the outside of 

 the pterotic crest; the smallest is the most ante- 

 rior of the three, lying along the crest and usually 

 more elongate in shape. 



The lengths and widths of the pterotic spines 

 vary among the species. In eight species (brasili- 

 ensis, guttatus, koreanus (Fig. 18a), multiradi- 

 atus, plurilineatus , regalis, semifasciatus , and 

 tritor), there is essentially no pterotic spine, 

 merely a rounded posterior area of the skull. In 

 six species (concolor (Fig. 18b), lineolatus, macu- 

 latus, munroi (Fig. 17b), niphonius, and sierra), 

 there is a blunt posteriorly projecting spine. 

 Scomberomorus sinensis is similar to this group, 

 but the posterior projection is broader and less 

 like a spine. The pterotic spines are longest in 

 three species (cavalla, commerson (Fig. 17a), and 

 queenslandicus), all of which also have promi- 

 nent posterior projections of the intercalars. 

 Grammatorcynus (Fig. 19b) is similar to the lat- 

 ter group, but the spine is thinner and sharper. 

 Acanthocybium (Fig. 19a) has a longer and thin- 

 ner pterotic spine than do Grammatorcynus and 

 the species of Scomberomorus. 



Sphenotics. — The sphenotics form the most 

 posterior dorsolateral part of the roof of the orbit. 

 They continue the outer lateral shelf from the 

 frontals and articulate with the pterosphenoid 

 medially and the prootic and pterotic posteriorly. 

 A segment of the articular fossa for the head of 

 the hyomandibula is afforded by the lateral wall 

 of the sphenotic on the ventral surface. The 

 sphenotic is pierced by a foramen for the ramus 

 oticus nerve (Allis 1903). When viewed dorsally, 

 the sphenotics spread out on both sides more 

 prominently in Scomberomorus than in Acan- 

 thocybium, as noted by Devaraj (1977). Devaraj 

 stated that the "midlateral projection" was large 

 in koreanus, guttatus, maculatus, and regalis; 

 small in lineolatus, cavalla, and commerson; and 

 absent in Acanthocybium, but we are not clear as 

 to what he was referring. 



Intercalars. — The intercalars (opisthotics) are 

 flat bones that form part of the posterior border of 

 the neurocranium interposed between the pter- 

 otics and exoccipitals. The anterior portion on the 

 dorsal surface is concealed by the overlapping 

 pterotic, thus exposing the bone on the dorsal 

 surface less than on the ventral side. Each inter- 

 calar bears a protuberance on the dorsal surface 

 to receive the lateral arm of the posttemporal. 

 This protuberance is followed by a posterior 

 projection of the intercalars in some species of 

 Scomberomorus but not in Acanthocybium or 

 Grammatorcynus. 



Species of Scomberomorus may be roughly di- 

 vided into three groups based on the size of 

 the posterior projection from the intercalar as 

 Devaraj (1977) noted for Indian species. Eight 

 species lack any posterior projection or have only 

 an insignificant projection: guttatus, koreanus 

 (Fig. 18a), lineolatus, multiradiatus , munroi 

 (Fig. 17b), plurilineatus, semifasciatus, and si- 

 nensis. In each of these species, except S. multi- 

 radiatus, the pterotic spine protrudes further 

 posteriorly than does the intercalar region. In S. 

 multiradiatus, the posterior corners of the skull 

 are rounded and there is no pterotic spine so the 

 intercalars project further posteriorly. Eight spe- 

 cies have a distinct posterior projection from the 

 intercalar: brasiliensis , cavalla, concolor (Fig. 

 18b), maculatus, niphonius, regalis, sierra, and 

 tritor. The posterior projection is smaller in some 

 specimens of S. niphonius, placing it somewhat 

 between groups 1 and 2. The posterior projection 

 is a little longer in S. cavalla, between groups 

 2 and 3. Two species, commerson (Fig. 17a) 



574 



