24 



Fishery Bulletin 90(1). 1992 



opening of the posterior myodome. These flanges are 

 longer in G. bilineatus (18-21% of neurocranium 

 length) than in G. bicarinatus (14%), making the 

 posterior opening of the posterior myodome larger in 

 G. bilineatus (Fig. 8). A ventrally projecting median 

 keel is present in the area anterior to the origin of the 

 lateral flanges. In ventral view, the parasphenoid nar- 

 rows posteriorly until near the region of the median 

 keel, where it widens slightly before the lateral wings. 

 The anterior portion and the region just anterior to the 

 lateral wings are about equal in width. In Gramma- 

 torcynus, the shaft of the parasphenoid is narrower 

 than that of Scomberomorus and Acanthocybium. In 

 G. bilineatMS, the contour of the parasphenoid is con- 

 cave, making the orbit larger than in G. bicarinatus, 

 in which the parasphenoid is flat (Fig. 7). 



BasioccJpital The basioccipital has lateral 

 flanges on either side of the skull and forms the roof 

 and lateral walls of the posterior myodome. The lateral 

 flanges expand ventrally to meet the flat posterior 

 flanges of the parasphenoid. Anteriorly, the basi- 

 occipital is attached to the prootics and dorsally with 

 the exoccipitals. The first vertebral centrum attaches 

 to the posterior surface of the basioccipital. 



Exoccipital The exoccipitals connect the skull 

 with the first vertebra dorsally. The exoccipital artic- 

 ulates with the epiotic and supraoccipital bones antero- 

 dorsally, the intercalars laterally, and with the other 

 exoccipital posterodorsally. In ventral view, the ex- 

 occipital articulates with the prootic anteriorly, basi- 

 occipital ventromedially, and intercalar laterally. In 

 posterior view, the foramen magnum is framed by the 

 exoccipitals. 



Branchiocranium The branchiocranium is divided 

 into five sections: mandibular arch, palatine arch, 

 hyoid arch, opercular apparatus, and branchial 

 apparatus. 



Mandibular arch The man- 

 dibular arch is composed of the 

 upper jaw (premaxilla, maxilla, 

 and supramaxilla) and the lower 

 jaw (dentary, angular, and retro- 

 articular). Teeth are borne on the 

 premaxilla and dentary, and the 

 number of teeth on these bones 

 differs between species. 



Dentition Long, thin, 

 slightly laterally compressed 

 teeth are present in a single row 

 in the upper and lower jaws of 

 Grammatorcynus. Scomberomo- 

 rus has large, triangular, lateral- 

 ly compressed teeth similar to 

 those of Acanthocybium, which 



are blunter and more tightly compressed. The length 

 of the jaw teeth differs between the species: G. bica- 

 rinatus has longer teeth than G. bilineatus (maximum 

 length 6% vs. 4% dentary length). The number of jaw 

 teeth in Grammatorcynus also varies. Teeth are often 

 broken or lost, so the range in mean tooth count may 

 not reflect accurately the actual number of teeth. 

 However, the maximum number of teeth is useful. 

 Grammatorcynus bicarinatus has a lower maximum 

 tooth count on its upper jaw than G. bilineatus (25 vs. 

 37), and the same is true of the lower jaw, (23 vs. 32; 

 Table 2). The maximum number of jaw teeth present 

 in Scomberomorus is slightly higher than G. bilineatus 

 (39, range 5-39 in the upper jaw; and 37, range 4-37 

 in the lower jaw). Collette and Russo (1985b) noted that 

 in Scomberomorus, the species with the fewest teeth 

 has the fewest gill rakers and the species with the most 

 teeth has the most gill rakers. There is a similar cor- 

 relation in Grammatorcynus: G. bilineatus also has 

 more gill rakers (18-24 vs. 12-15 in G. bicarinatus). 

 Premaxilla The premaxilla (Fig. 11) is a long, 

 curved bone with an arrowhead-shaped anterior end 

 that extends dorsally and posteriorly as an ascending 

 process. The posterior shank of the premaxilla is 

 elongate and bears a row of 14-37 long, thin teeth on 

 its ventral margin. There are two articular facets for 

 the overlying maxilla at the junction of the posterior 

 margin of the ascending process with the shank por- 

 tion. Ascending processes of both premaxillae are 

 closely approximated to each other mesially and fit into 

 the median groove of the ethmoid bone. The ascend- 

 ing process forms an angle of 55-67° with the shank: 

 G. bilineatus has a slightly larger angle (60-67°, Fig. 

 lie) than G. bicarinatus {bb-bi° , Fig. lid). Gramma- 

 torcynus has a larger angle than any species of Scom- 

 beromorus excepts, guttatus (60-61°). The ascending 

 process is 33-40% of the total length of the premax- 



