56 ELOPIFORM FISHES 



of the anterior ceratohyal. A foramen on the medial surface of the upper hypohyal 

 connects with the arterial canal : the significance of this foramen is not clear. 



A tooth plate is associated with the dorsal margin of the anterior ceratohyal and 

 part of the upper hypohyal. Additional tooth plates are scattered in the skin 

 covering the medial surface of the anterior ceratohyal. 



There are 21-24 branchiostegal rays. The anterior 13 are thin and pointed 

 (almost filiform) and attached to the ventral margin of the anterior ceratohyal 

 which is scalloped for their reception. As one passes back along the series the rays 

 become spathiform (terminology after McAllister 1968) and are attached to the 

 lateral surface of the posterior ceratohyal. The upper branchiostegal extends further 

 forward than those preceding it and is more closely associated with the interoper- 

 culum. 



The gill arch structure is primitive for a teleostean fish. For instance, the basi- 

 branchial complex is formed by independent dermal and endochondral elements 

 and the tooth plates associated with the cerato- and epibranchials are very small and 

 numerous. 



The basibranchial complex is formed by an ossified basihyal succeeded by three 

 ossified basibranchials. The first basibranchial is short and deep and set slightly 

 below the level of the elongate second and third elements. The fourth basibranchial 

 is represented by cartilage. Tooth plates associated with the basihyal and basi- 

 branchial are an elongated basihyal plate succeeded by a long tooth plate overlying 

 the first three basibranchials. The tooth plate overlying the fourth basibranchial 

 varies in shape and size from specimen to specimen : in young adults there are two 

 ovoid tooth patches set one behind the other, but in old specimens only a single plate 

 is recognizable. Thus, throughout life there is some degree of assimilation (Nelson 

 1969a : 484). 



Hypobranchials 1-3 are attached to the posterior edge of their respective basi- 

 branchial supports. There are five ceratobranchials and four epibranchials, the 

 fourth epibranchial with a large expansion posteriorly. There is no fifth epibranchial 

 as figured for Megalops by Holstvoogd (1965 : fig. 3b). Of the four infrapharyngo- 

 branchials the anterior three are ossified and the fourth is represented in cartilage. 

 The first infrapharyngobranchial articulates with the parasphenoid. Supra- 

 pharyngobranchial 1 is ossified and attached to the dorsal limb of epibranchial 1 by 

 cartilage. 



Tooth plates of the first arch are associated with hypo-, cerato-, epi- and infra- 

 pharyngobranchials. Gill-rakers are present, associated with all the above elements 

 except the first and fourth infrapharyngobranchials. On the first arch there is a 

 total of 62 gill-rakers (16 on the hypobranchial, 24! upon the ceratobranchial, 20^ 

 on the epibranchial and 1 lying free between the epibranchial and infrapharyngo- 

 branchial). Immediately behind the gill-rakers and resting upon a ledge near their 

 base there is a single row of rectangular tooth plates. On the ceratobranchial and 

 much of the epibranchial there is a one-to-one correspondence between tooth plate 

 and gill-raker. At the top of the epibranchial the tooth plate row breaks into 

 smaller irregular plates which continue in the dermis overlying the infrapharyngo- 

 branchial. Over the hypobranchial the tooth plate row has consolidated into larger 



