34 



Fishery Bulletin 90|1). 1992 



converge posteriorly from the anterior projection on 

 the lateral side of the bone. The upper ridge articulates 

 with the lower posterior projection of the opercle, and 

 the lower ridge connects to the posterodorsal margin 

 of the interopercle. The dorsal ridge is much more 

 prominent than the ventral ridge and extends over the 

 main part of the subopercle as a discrete shelf. The 

 weaker ventral ridge is more difficult to detect in most 

 specimens of Grammatorcynus. The angle between the 

 anterior projection and the anterior margin of the 

 subopercle is acute in Grammatorcynus and S. multi- 

 radiatus; however, in Acanthocybium and the other 

 species o{ Scomberomonis the angle is close to 90°. The 

 length of the anterior projection in Grammatorcynus 

 varies from 23 to 33% of the length of the anterior 

 margin dorsal to the projection. The projection is slight- 

 ly longer (28-33%) in G. bicarinatus than in G. biline- 

 atus (23-28%). The projection is longest in Acan- 

 thocybium (36-45%) and shortest in S. commerson 

 (20-25%), with the rest of the species of Scombero- 

 morus having projections between 21 and 43%. 



Interopercle The interopercle is roughly oval 

 in shape, narrow at the anterior margin and widening 

 posteriorly, with a crest on the superior margin 

 (Collette and Russo 1985b: fig. 35). There is a well- 

 developed facet on the mesial side to receive the artic- 

 ular process of the interhyal. The maximum depth of 

 the interopercle relative to the length of the bone is 

 35-43% in Grammatorcymis. The maximum depth of 

 the interopercle is a little greater in Acanthocybium 

 (40-49%), and much greater in the species of Scom- 

 beromorus (45-61%). Often there is a well-formed 

 notch anterior to the crest on the sloping anterior 

 margin in Grammatorcynus and Scomberomorus, 

 which is not as well developed in Acanthocybium. The 

 posterior margin is rounded in Grammatorcynus and 

 Scomberomorus but divided into two by a notch in 

 Acanthocybium. 



Branchial apparatus The branchial apparatus is 

 composed of five pairs of gill arches, gill filaments, gill 

 rakers, pharyngeal tooth patches, and supporting 

 bones. The general arrangement in Grammatorcynus 

 is similar to that found in other scombrids such as the 

 Sardini (Collette and Chao 1975), Thunnus (Iwai and 

 Nakamura 1964:22, fig. 1; de Sylva 1955:21, fig. 40), 

 Scomberomorus (Mago Leccia 1958:327, pi. 12; Collette 

 and Russo 1985b: fig. 36), and Rastrelliger (Gnana- 

 muttu 1971:14, fig. 6). Most branchial bones bear 

 patches of tiny teeth. 



Baslbranchials The three basibranchials form 

 an anteroposterior chain. The first and second are 

 about the same size, and considerably shorter than the 

 third. The first is covered dorsally by the glossohyal. 

 In lateral view, the first basibranchial is narrowest 

 in the middle. In Grammatorcynus and Acantho- 



cybium it is elongate. In Scomberomorus it is short with 

 a wide base where it joins with the second basibran- 

 chial. The second basibranchial has a prominent notch 

 in the ventral margin and a distinct groove laterally 

 that extends from the anteroventral margin to the mid- 

 dorsal region of the bone. This groove accepts the 

 anterior end of the first hypobranchial. The third 

 basibranchial has an expanded anterior end at its junc- 

 tion with the second basibranchial, and then tapers 

 posteriorly. A prominent groove is present anteriorly 

 that accepts the medial anterior end of the second 

 hypobranchial. A section of cartilage extends poster- 

 iorly to articulate with the fourth and fifth cerato- 

 branchials. 



Hypobranchial Three hypobranchials are pres- 

 ent. The first is interposed beween the second basi- 

 branchial and the first ceratobranchial. The second is 

 about the same size as the first, fits into a groove on 

 the third basibranchial, and extends to the second 

 ceratobranchial. The third hypobranchial is smaller 

 than the first or second, fits snugly against the pos- 

 terolateral margin of the third basibranchial, and its 

 posterior end articulates with the third ceratobranchial. 



Ceratobranchlals The five ceratobranchials 

 are the longest bones in the branchial arches. They 

 have a deep groove ventrally for the branchial arteries 

 and veins. The ceratobranchials support most of the 

 gill filaments and gill rakers. The first three are mor- 

 phologically similar and articulate with the posterior 

 ends of their respective hypobranchials. The fourth is 

 more irregular and attaches to a cartilage posterior to 

 the third basibranchial. The fifth ceratobranchial is also 

 attached to the cartilage, has a dermal tooth plate fused 

 to its dorsal surface, and the complex is termed the 

 lower pharyngeal bone. It is covered with small con- 

 ical teeth that are directed slightly posteriad. 



Epibranchials The posterolateral end of each 

 of the four epibranchials is attached to the ends of the 

 first four ceratobranchials. Each epibranchial bears a 

 groove posterodorsally for the branchial arteries and 

 veins. The first epibranchial is the longest and bears 

 two processes mesially. The anterior process articulates 

 with the first pharyngobranchial, and the posterior 

 process attaches with the interarcual cartilage. The 

 second epibranchial is similar to the first, but slightly 

 shorter. The anterior end has two processes, an anter- 

 ior process that attaches to the second pharyngo- 

 branchial and a posterior process that is coupled with 

 the third pharyngobranchial by way of an elongate 

 cartilage. This process is relatively elongate in Gram- 

 matorcynus, but shorter in Acanthocybium and Scom- 

 beromorus. The third epibranchial is the shortest in the 

 series. Laterally, it is attached with the third cera- 

 tobranchial; mesially, it is attached with the third 

 pharyngobranchial. An elongate posterodorsal process 



