38 



Fishery Bulletin 90(1). 1992 



Posttemporal The posttemporal (Fig. 22) is a flat 

 elliptical bone with two sturdy anterior processes that 

 attach the pectoral girdle to the neurocranium. The 

 median (dorsal) process articulates with the dorsal sur- 

 face of the epiotic. The lateral (ventral) process is 

 shorter, round in cross section, and its hollow anterior 

 end articulates with the dorsal protuberance of the 

 intercalar. There is a thin shelf visible between these 

 two processes in G. bicarinatus (Fig. 22d) and Scom- 

 beromorus (Fig. 22a), but this shelf is hidden behind 

 the flat, posterior portion of the bone in G. bilineatus 

 (Fig. 22c) and Acanthocybium (Fig. 22b). A variably- 

 sized notch is present at the middle of the posterior 

 edge of the flat body of the bone. Grammatorcynus 

 usually has a distinct, variably-sized anteriorly directed 

 spine on the ventral margin of the median process 

 about one-third of the distance from the body of the 

 bone to the anterior tip of the process. In Acantho- 

 cybium, there is a separate process extending anterior- 

 ly from the ventral wall of the median process. This 

 auxiliary process (Kishinouye 1923) is as long or almost 

 as long as the median process itself. It ends in a series 

 of several pointed processes. (Both Conrad 1938 and 

 Devaraj 1977 referred to the auxiliary process as the 

 median process.) The lengths of the median and lateral 

 processes vary among the species under discussion. The 

 lengths were measured from the midpoint of the shelf 

 that connects the two processes, to the end of the pro- 

 cesses. Both the median and lateral processes are 

 longer, relative to the length of the entire bone, in 

 G. bilineatus where the shelf is hidden posteriorly 

 (median process is 53-60% length of entire bone, and 

 lateral process is 35-40%) than in G. bicarinatus where 

 the shelf is not hidden, and is found more near the mid- 

 point of the bone (median process is 49% and lateral 

 process is 30%). In Acanthocybium (shelf hidden) the 

 median process is 56-65% the length of the entire bone, 

 and the lateral process is 27-37%. In Scomberomorus 

 (shelf evident) the median process is 36-51% and the 

 lateral process is 15-36%. 



Another useful taxonomic character is the presence 

 (if present, shape is important) or absence of a spine 

 or process at the base of the lateral process on the inner 

 surface of the posttemporal. It is present as a wide flap 

 in Grammatorcynus (Fig. 22c, d), a blunt process in 

 Acanthocybium (Fig. 20b), and as a shelf with a point 

 in S. commerson, S. munroi, S. niphonius, S. pluri- 

 lineatus (Fig. 22a), and sometimes in S. sinensis. It is 

 absent or small and inconspicuous in the other 13 

 species of Scomberomorus. 



Supracleithrum The supracleithrum is an ovate 

 bone, overlapped dorsolaterally by the posttemporal 

 and overlapping the anterior part of the dorsal wing- 

 like extension of the cleithrum. The anterior border of 

 the bone on the mesial side is thickened into a ridge. 



median process 



lateral process 



auxiliary process 



Figure 22 



Lateral view of left posttemporals. (a) Scomberomorus 

 plurilineatus, South Africa, 910mm FL, Ix; (b) Acan- 

 thocybium solandri, Revillagigedos Is., 1068mm FL, 1 x ; 

 (c) Grammatorcynus bilineatus, Queensland, 521 mm 

 FL, 1.5 X ; (d) G. bicarinatus. Western Australia, 565 mm 

 FL. 



Dorsally there is a small handle-shaped process that 

 curves into the posterior margin to end in a notch at 

 the posterodorsal aspect. Both the anterior and pos- 

 terior borders are extended so that they form humps 

 in Grammatorcynus (Collette and Russo 1985b: fig. 41). 

 A branch of the lateralis system extends from the 

 posterior notch of the posttemporal onto the supra- 

 cleithrum. This short canal lies ventral to the dorsal 

 process of the supracleithrum and extends to the 

 posterior edge of the bone. 



