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Fishery Bulletin 90(1), 1992 



first basibranchial bone at the 

 anterior end of the branchial 

 arch. In Grammatorcynus there 

 is a quadrangular to oval tooth 

 plate fused to and covering the 

 dorsal surface of the glossohyal 

 (Collette and Russo 1985b: fig. 

 30). No tooth plate is present in 

 Acanthocybium or Scomberomo- 

 rus. The glossohyal of Gramma- 

 torcynus is slightly wider (width 

 47-55% of length) than the 

 roughly rod-shaped or conical- 

 shaped glossohyal of Scombero- 

 morus (35-54%) and the flat- 

 tened spatulate glossohyal of 

 Acanthocybium (42%). 



Urohyal The urohyal is a 

 compressed, median, unpaired 

 bone (Fig. 20). The anterior end 

 of this element lies between, and 

 is connected with, the hypohyals 

 of the left and right sides. The 

 most prominent difference in the 

 urohyal of Grammatorcynus is 

 that in dorsal view, the posterior 

 end of the dorsal margin is tri- 

 partite (Fig. 20c-d) instead of 

 forked, as it is in Scomberomorus 

 and Acanthocybium (Fig. 20a-b). 

 The dorsal and anterior portions 

 of the ventral margins are thick- 

 ened in Grammatorcynus. The 

 anterior end has an articulation 

 head; the posterior end is deepest 

 in Scomberomorus, and much 

 less deep in Grammatorcynus 

 due to the convex shape of the 

 ventral margin. The maximum 

 depth of the urohyal in Gramma- 

 torcynus is 15-20% of the length 

 of the dorsal margin. The max- 

 imum depth in Acanthocybium is 

 not as great as this (13-15%), and in Scomberomorus 

 it is greater (16-24%). In Grammatorcynus the ven- 

 tral margin of the urohyal is relatively short, only 

 68-71% of the length of the dorsal margin, compared 

 with 80-91% in Acanthocybium and Scomber orfiorus. 



Opercular apparatus Four wide, flat bones 

 (opercle, preopercle, subopercle, and interopercle) fit 

 together to form the gill cover. 



Opercle The opercle (Fig. 21) is overlapped 

 laterally on its anterior margin by the posterior half 

 of the preopercle. The narrow, elongate, articular facet 



Figure 20 



Urohyals in left lateral view, (a) Scomberomorus queenslandicus, Queensland, 641 mm 

 FL; (h) Acanthocybium solandri, Indian 0., 1088mm FL; (c) Grammatorcymis bilineatiis, 

 New Guinea, 382 mm FL; (d) G. bicarinatus, Australia, 663 mm FL. Fig. (a) drawn 

 twice as large as (b), (c) three times as large. Inset is the posterior end of the dorsal 

 margin, in dorsal view. 



for the opercular process of the hyomandibula is located 

 on the medial surface of the anterodorsal corner of the 

 opercle. Grammatorcynus and most species of Scom- 

 beromorus have a weak process at the posterodorsal 

 corner. This process is absent in Acanthocybium. In 

 Grammatorcynus the width of the opercle is 63-79% 

 of the total length of the bone; G. bicarinatus has a 

 wider opercle (width 72-79% of length. Fig. 21d) than 

 G. bilineatus (63-72%, Fig. 21c). Both species of Gram- 

 matorcynus have narrow opercles compared with the 

 extremely wide opercles found in Acanthocybium 

 (Fig. 21b). 



