COLLETTE and RUSSO: SPANISH MACKERELS 



margin is tripartite (Fig. 31d) instead of forked. 

 Some specimens of Acanthocybium differ from 

 the other two genera by having a slight indenta- 

 tion in the anterior end of the urohyal. 



OPERCULAR APPARATUS.— Four wide flat 

 bones (opercle, preopercle, subopercle, and inter- 

 opercle) fit together to form the gill cover which 

 protects the underlying gill arches. 



Opercle. — The opercle is broad (Fig. 32), and it 

 is overlapped laterally on its anterior margin by 

 the posterior half of the preopercle. The narrow, 

 elongate, articular facet for the opercular process 

 of the hyomandibula is located on the mesial 

 surface of the anterodorsal corner of the opercle. 

 Grammatorcynus (Fig. 32d) and most species of 

 Scomberomorus have a weak process at the pos- 

 terodorsal corner. This process appears to be 

 absent in Acanthocybium (Fig. 32c) and Scom- 

 beromorus sinensis. In several species of Scom- 



beromorus (caualla, regalis, and tritor), there is 

 also a weak anteroventral process. Instead of a 

 distinct process at this point, Acanthocybium and 

 the other species of Scomberomorus have an 

 angle where the anterior margin meets the ante- 

 roventral margin. The posterior margin and/or 

 the posteroventral margin of the opercle are 

 fimbriate in Acanthocybium and most species of 

 Scomberomorus (brasiliensis, koreanus, lineola- 

 tus, maculatus, niphonius , queenslandicus , semi- 

 fasciatus (Fig. 32a), sinensis, and tritor). Gram- 

 matorcynus (Fig. 32d) has a much narrower and 

 more elongate opercle than do Acanthocybium 

 or the species of Scomberomorus. The most elon- 

 gate opercle among Scomberomorus species is in 

 S. multiradiatus (Fig. 32b). The broadest is in 

 Acanthocybium. 



Preopercle. — The preopercle (Fig. 33) is a large 

 crescent-shaped flat bone, broadest at the lower 

 posterior angle. The anterior portion of the bone 



FIGURE 32. — Left opercles in lateral view, 

 a. Scomberomorus semifasciatus, New Guin- 

 ea, 510 mm FL. b. Scomberomorus multi- 

 radiatus , New Guinea, 294 mm FL. c. Acan- 

 thocybium solandri, Revillagigedos Is., 1,080 

 mm FL. d. Grammatorcynus bilineatus, 

 Marshall Is., 424 mm FL. 



a 



589 



