22 



Fishery Bulletin 90(1). 1992 



a 



Figure 9 



Outline of pterosphenoid opening on ventral side of 

 skull in Grammatorcynus. (a) G. bilineatus, Scott 

 Reef, Timor Sea, 453 mm FL; (b) G. bicarinatus, 

 Western Australia, Exmouth Gulf, 765mm FL. 



infraorbital. It has a large, mesial, shelflike extension 

 (subocular shelf of Smith and Bailey 1962). The fourth 

 through penultimate elements total 13 in a specimen 

 of G. bilineatus (Fig. 10c), are small, and are easily lost 

 with cheek scales during dissection. No special effort 

 was made to compare these bones in the two species. 



Otic region This region encloses the otic cham- 

 ber inside the skull, and is formed by the parietal, 

 epiotic, supraoccipital, prootic, pterotic, sphenotic, and 

 intercalar (opisthotic) bones. 



Parietals The parietals articulate with the 

 frontals anteriorly, the supraoccipital mesially, the 

 pterotics laterally, sphenotics ventrally, and epiotics 

 posteriorly. There is a short inner lateral crest on the 

 parietals and epiotics, but this crest does not originate 

 on the frontals as it does in Scomberomorus and 

 Acanthocybium. 



Epiotics The epiotics are irregular bones 

 bounded by the parietals anteriorly, the supraoccipital 

 mesially, the exoccipitals posteriorly, and the pterotics 

 laterally. The medial process of the posttemporal bone 

 attaches to a distinct roughened process on the 

 posterior corner of the epiotic. Scomberomorus has a 

 roughened area at the posterior end of the fronto- 

 epiotic crest rather than a distinct process. 



Supraoccipital The supraoccipital forms the 

 dorsomedian portion of the posterior end of the neuro- 

 cranium. It bears a well-developed crest that continues 

 forward onto the parietals but stops at the pineal 



opening instead of extending all the way forward onto 

 the frontals as in Scomberomorus. The supraoccipital 

 consists of a thin crest on a roughly hexagonal base. 

 The crest extends down over the exoccipitals along the 

 median line where the dorsal walls of the exoccipitals 

 suture with each other. It extends posteriorly over the 

 first vertebral centrum (Fig. 7). 



Prootics In ventral view (Fig. 8), the prootics 

 connect with all the bones in the posterior part of the 

 neurocranium. Each prootic is bordered ventrally by 

 the parasphenoid; posteriorly by the basioccipital, ex- 

 occipital, and intercalar; laterally by the pterotic and 

 sphenotic; and anteriorly by the parasphenoid and 

 basisphenoid. The prootics are irregular in shape and 

 meet each other along the ventromedian line of the 

 brain case to form the posterior portion of the 

 myodome. 



Pterotics The pterotics form the lateral pos- 

 terior corners of the neurocranium. Each pterotic is 

 produced posteriorly to form a spine. A pterotic ridge 

 continues anteriorly onto the parietal, but does not 

 extend onto the posterior part of the frontal as it does 

 in Scomber om^orus. In ventral view (Fig. 8), the 

 pterotics articulate with the sphenotics anteriorly and 

 the prootics and intercalars medially. 



Sphenotics The sphenotics form the most pos- 

 terior 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 fossa at the junc- 

 ture of the sphenotic and pterotic receives the anterior 

 condyle of the hyomandibula. In dorsal or ventral view, 

 the distance between the tips of the two sphenotics is 

 the widest portion of the cranium, 60-67% the length 

 of the neurocranium in Grammatorcynus. 



Intercalars The intercalars (opisthotics) are flat 

 bones that form part of the posterior border of the 

 neurocranium interposed between the pterotics and ex- 

 occipitals. The anterior portion on the dorsal surface 

 is concealed by the overlapping pterotic, thus expos- 

 ing the bone on the dorsal surface less than on the 

 ventral surface (compare in Figures 6 and 8). Each 

 intercalar has a roughened area on its dorsal surface 

 to receive the lateral arm of the posttemporal. There 

 is no posterior projection from the intercalars in Gram- 

 matorcynus or Acanthocybium as there is in eight 

 species oi Scomberomonis, such as S. commerson and 

 S. concolor (Collette and Russo 1985b: figs. 11a and 

 12b). 



Basicranlal region This region consists of the 

 parasphenoid, basioccipital, and exoccipital bones, and 

 forms the posteroventral base of the skull. 



Parasphenoid The parasphenoid is a long, 

 cross-shaped bone. It articulates with the vomer ante- 

 riorly and forms the ventral axis of the skull. It also 



