Collette and Gillis: Osteological differences between two species of Orammatorcynus 



39 



The maximum width of the supracleithrum varies 

 from 43 to 75% of the total length of the bone in the 

 three genera. It is widest in Gram.matorcynus, width 

 72-82% (89% in one 475 mm FL specimen oibilineatus) 

 of length (due to the extensions of anterior and pos- 

 terior borders). Scomberomorus varies in width from 

 43% in S. multiradiatus to 62% in S. nipkonius. There 

 is no evidence that size is a factor in the size of the 

 supracleithrum in Grammatorcynus as was noted by 

 Collette and Russo (1985b) for Scomberomorus. 



The dorsal process is prominent in Grammatorcynus, 

 S. cavalla, S. commerson, S. lineolatus, and especially 

 in Acanthocybium. In other species oi Scomberomorus, 

 it is either small or less sharply set off from the main 

 body of the supracleithrum. 



Supratemporal The supratemporal is a thin flat 

 bone having three distinct arms and lying just under- 

 neath the skin where its lateral arm articulates with 

 a dorsal articular surface on the pterotic. The anterior- 

 most arm is the longest, while the ventrally directed 

 arm is the shortest. The arm directed posteriorly is 

 intermediate in length. The anterior margin is deeply 

 concave, and the greatly convex posterior margin 

 slightly overlaps the dorsal arm of the posttemporal. 



The supratemporal bears a prominent lateral line 

 canal that extends out almost to the tips of all three 

 arms (Collette and Russo 1985b: fig. 42). In these three 

 genera, the canal along the anterior margin of the bone 

 is the longest, and the canal along the lateral side is 

 next longest. In Grammatorcynus, the first canal is not 

 branched like it is in most species of Scomberomorus, 

 and the second canal is relatively longer. 



Cleithrum The main body of the cleithrum is cres- 

 cent-shaped with an anterodorsal spine and a posterior- 

 ly projecting plate at the upper end (Collette and Russo 

 1985b: fig. 43). The angle between the spine and the 

 plate is much smaller in Grammatorcynus and Scom- 

 beromorus than in Acanthocybium. In Grammatorcy- 

 nus, the spine does not extend as far dorsally as the 

 plate. In Acanthocybium and most species of Scombero- 

 morus, the spine extends about equally as far dorsally 

 as the plate, and in S. sinensis the spine extends well 

 beyond the dorsal margin of the plate. In Gramma- 

 torcynus and most species ot Scomberomorus, the plate 

 narrows posteriorly. The posterior plate is longer and 

 of uniform width in Acanthocybium. 



The lower part of the cleithrum is large and folded 

 back upon itself as two walls: one lateral and the other 

 mesial, which meet at their anterior margins and run 

 parallel to each other. The mesial wall of the cleithrum 

 forms a large triangular slit with the coracoid. In 

 Grammatorcynus and Scomberomorus, the lateral wall 

 of the cleithrum is narrow enough to allow part of the 

 slit to be visible in a lateral view. This slit is hidden 



in lateral view in the species oi Scomberomorus because 

 of the great width of the lateral wall of the cleithrum 

 (Devaraj 1977:46, Collette and Russo 1985b: figs. 



43a-b). 



Coracoid The coracoid is elongate and more or less 

 triangular in shape. It connects wath the scapula along 

 its dorsal edge and with the mesial shelf of the cleith- 

 rum anterodorsally and an tero ventrally. The coracoid 

 is relatively wider in Grammatorcynus and Scombero- 

 morus than in Acanthocybium. 



Scapula The anterior margin of the scapula con- 

 nects to the mesial shelf of the cleithrum. This attach- 

 ment extends to the posterior projecting plate antero- 

 dorsally. The scapula is attached to the coracoid 

 posteriorly and with the first two radials posterodor- 

 sally. The posterodorsal margin of the scapula is drawn 

 out into a facet that accepts the most anterior ray of 

 the pectoral fin. The scapula is pierced by a large, usual- 

 ly round, foramen near the lateral margin with the in- 

 ner shelf of the cleithrum. A prominent suture leads 

 to the dorsal and ventral margin of the scapula from 

 the foramen. The suture is intermediate in size in 

 Gram.matorcynus relative to the large sutures present 

 in Acanthocybium, S. brasiliensis, andS. regalis, and 

 the small suture in S. koreanus. 



Radials The four radials differ in size and shape and 

 attach directly to the thickened posterior edges of the 

 scapula and coracoid. The size of the radials increases 

 posteroventrally. Small foramina are located beween 

 the 2nd and 3rd and the 3rd and 4th radials counting 

 posteriorly. In Gramynatorcynus the first two radials, 

 and sometimes a small portion of the third, attach to 

 the scapula; the second two, sometimes only one and 

 a large portion of the second, attach to the coracoid. 

 In Acanthocybium. and Scomberomorus the upper one- 

 third of the third radial, along with the first two radials, 

 always attaches to the scapula, and the ventral two- 

 thirds of the third radial plus the fourth radial attach 

 to the coracoid. A much larger foramen is present 

 between the largest (fourth) radial and the coracoid. 

 Posteriorly, this foramen is framed by a posterior 

 process of the upper part of the fourth radial meeting 

 an anterior process from the posterior margin of the 

 coracoid. This process is only slightly developed in 

 Grammatorcynus. The foramen is about equal in size 

 to, or larger than the scapular foramen in Gramyna- 

 torcynus and Scomberomorus, whereas in Acantho- 

 cybium the scapular foramen is much larger. 



Pectoral fin rays The first (uppermost and largest) 

 pectoral fin ray articulates directly with a posterior 

 process of the scapula. The other rays attach to the 

 radials. The number of pectoral rays varies from 19 to 

 26 in the three genera. Grammatorcynus has 21-26 



