58 ELOPIFORM FISHES 



Opercular series. The greatest width of the operculum occurs at the level of the 

 articulation with the hyomandibular. Above the articulation the anterior margin 

 of the operculum is concave. The posterior border of the bone is smoothly rounded. 

 Postero-ventrally the ventral margin is obliquely inclined. The suboperculum is 

 essentially a parallel-sided bone with rounded anterior and posterior margins. The 

 interoperculum is large and rhomboidal in shape. It is attached to the articular 

 by a stout ligament. 



The preoperculum has a smoothly concave anterior border. Mid-way along its 

 length there is a small prominence anteriorly for the insertion of part of the adductor 

 mandibulae muscle. The preoperculum is expanded postero-ventrally. 



Cephalic sensory canal system. The supraorbital canal penetrates the frontal 

 above the autosphenotic spine and curves anteriorly to run within the shallow ridge. 

 A large backwardly directed branch of the canal runs within the posterior part of the 

 ridge to open on to the parietal. Within the frontal the main secondary branches 

 of the canal are as illustrated (Text-fig. 20) but in younger individuals the branches 

 are far more numerous. 



A large otic sensory canal runs along the lateral border of the pterotic 

 opening anteriorly above the autosphenotic spine and posteriorly above the posterior 

 limit of the hyomandibular facet. 



The infraorbital sensory canal runs near to the orbital margin of all infraorbitals 

 except the first where it passes diagonally across the bone to open at the base of the 

 antorbital. Short branches are given off posteriorly from the main canal. Within 

 the skin these canals extend for a considerable distance and exhibit prolific branching. 

 The infraorbital canal bifurcates as it leaves the anterior (dorsal) end of infraorbital I, 

 sending a thin antorbital branch (adnasal branch of some authors, e.g. Nybelin 

 1967a) backwards, and a larger canal forwards which runs through a rostral ossicle 

 before uniting with the ethmoid commissure (this region of the canal system has been 

 excellently described and figured by Nybelin 1967a). The infraorbital canal meets 

 the supraorbital and otic canals within the skin above the dermosphenotic. 



The preopercular sensory canal runs very close to the anterior border and opens 

 on to the surface of the bone through four to seven pores. 



The mandibular sensory canal pierces the posterior surface of the articular and 

 runs within this bone and the dentary. The canal opens to the surface by pores 

 which become more numerous anteriorly. 



Pectoral girdle and fin. The supratemporal is very similar to that of Elops 

 hawaiensis (p. 22). The pattern of the contained lateral line and supratemporal 

 commissure is also similar to Elops, with the difference that the commissure in Tarpon 

 has very few pores. 



The post-temporal is a large concavo-convex bone disposed in the vertical plane. 

 The anterior margin shows three projections, separated by two shallow indentations. 

 The medial (dorsal) projection overlies the dorso-lateral face of the epiotic process 

 to which it is attached by a ligament. The middle process is wide and truncated 

 anteriorly. To this limb is attached a stout ligament which runs into the post- 

 temporal fossa. The spine-like lateral (central) process is inclined antero-ventrally 

 and connects with the basal part of the intercalar by a stout ligament. 



