CABANGIDAE 41 



The opercular bones do not in general form such broad, smooth 

 areas as in the Scombridae. There are no preopercular serrations ex- 

 cept in the very young, and there is never an open sensory canal along 

 the preopercular ridge. When there is any indication of a sensory sys- 

 tem in the bone in this region it is in the form of very fine tubes. 

 Trachurus is somewhat of an exception to this in having much larger 

 Trachurus is somewhat of an exception to this in having much larger 

 tubes than in any of the other genera. 



The head of the hyomandibular, where it articulates with the 

 cranium, is more or less divided into two parts. In Gnathanodon the 

 parts are contiguous, or with only a slight notch between them. In 

 Elagatis they are remote from each other. Between these two degrees 

 of separation there are all intermediate conditions, though they are 

 usually at least slightly separated. The hyomandibular is channeled 

 behind to receive the preopercle, and sends back a process to support 

 the opercle. In Oligoplites the upper end of the hyomandibular bears 

 on its outer surface a large wing of bone, pointing forward as in 

 Caranx hippos (see under suborbitals), but there is no stay from the 

 suborbital ring attached to it. In Scomberoides this process is reduced 

 to a small, inconspicuous point. 



There is never any opening between the hyomandibular and 

 metapterygoid that frequently appears in Percoid fishes except in 

 Gnathanodon, and to a slight extent Trachurus. The condition in the 

 former genus is identical with that of Roccus. The metapterygoid 

 throws out a broad wing, which extends backward to near the pre- 

 opercular ridge, leaving a wide, open space behind it. In Trachurus 

 the wing is feebly developed, and it fits so closely against the hyo- 

 mandibular that the open space is scarcely apparent. No trace of it is 

 apparent in any of the others. 



The mesopterygoid forms a broad supporting shelf for the orbit. 



The symplectic extends for a considerable distance behind the 

 quadrate in a channel. 



Usually the pterygoid turns at a right angle and reaches forward 

 towards the prefrontal, as it does in the majority of fishes. The an- 

 terior end of the pterygoid, and often a small part of the posterior end 

 of the palatine is attached to the prefrontal. Often a small tubercle of 

 bone is developed on the pterygoid just behind this attachment. But 

 as the cranium becomes flexed downward and the face bones drawn 

 forward, as in some of the deep, compressed forms, the pterygoid is 

 directed nearly straight upward and finally even somewhat backward, 

 while the tubercle of bone becomes a long spur or process extending 



