FOSSIL AND RECENT 87 



The neural arches of the first ural and first preural centra are fused in Sedenhorstia, 

 producing a single median expansion which Goody (1969a : 19) suggested may be the 

 forerunner of a stegural. Megalopids and Elops always show distinct neural arches 

 on these two centra, but in older specimens of the Recent genera there is only a 

 slight indication of their individuality. It would therefore seem that the con- 

 solidation in Sedenhorstia is of minor significance. 



In the cranium there is a general resemblance to megalopids. The skull is 

 relatively deep with the quadrate/mandibular articulation beneath the orbit. S. 

 orientalis is unusual among the Sedenhorstia species in that the lower jaw articulation 

 occurs immediately behind the orbit. In this respect this species shows an inter- 

 mediate condition between Tarpon and Elops. The orbit of Sedenhorstia is rela- 

 tively large and the long basisphenoid pedicel in S. dayi suggests a deep myodome, as 

 in Megalops. The otic region of the neurocranium is relatively short, as in Megalops, 

 and the skull roof in this region exhibits a certain convexity suggesting large post- 

 temporal fossae. Recent megalopids show an open dilatator fossa which is deep in 

 the dorso-ventral plane. Such a fossa, also seen in Sedenhorstia, differs from the 

 shallow, roofed fossa in Elops. The Eocene megalopids more nearly resemble Elops 

 in this respect. 



The parasphenoid of Sedenhorstia appears to be edentulous. If teeth were present 

 they must have been very small and restricted to the mid-line beneath the basi- 

 sphenoid pedicel. A nearly edentulous parasphenoid is found in megalopids, but 

 not in Elops. 



The upper jaw shows a marked convexity along the oral border and is relatively 

 deep, with two very large supramaxillae. Anteriorly the maxillary head shows a 

 simple ethmoid projection immediately behind which there is a rounded process 

 articulating with the palatine. In all these features there is a close agreement with 

 the megalopids. A further megalopid feature of the upper jaw is the extension of 

 the premaxilla beyond the dermethmoid. The maxilla of S. orientalis resembles 

 that of Elops in its length, extending well behind the orbit. The lower jaw is similar 

 to Elops, Protarpon and Promegalops in remaining moderately shallow throughout 

 its length, with an ill-defined coronoid process. The Recent megalopids have a 

 prominent coronoid process, which is elongated antero-posteriorly. The teeth on 

 the dermal jaws are unusual among elopoids in being pointed and set in a single row. 



The circumorbital bones are relatively narrow and the fifth tapers dorsally, as in 

 megalopids. The fifth infraorbital is rectangular in Elops. The first infraorbital 

 shows a gently rounded dorsal margin, as in megalopids. In Elops the first infra- 

 orbital turns upwards to lie alongside the supraorbital. The number of infra- 

 orbitals is constant throughout the elopids and megalopids. Goody (1969a : fig. 1) 

 shows six infraorbitals (one more than is usual) in S. dayi but this appears to be an 

 error. 



In the opercular series the preoperculum is narrow with the dorsal limb inclined 

 antero-ventrally (or vertically in S. orientalis), as in megalopids. The preopercular 

 sensory canal opens to the surface by a series of large pores. In Elops the upper 

 preopercular limb is inclined postero-ventrally and the sensory canal opens by a 

 series of short secondary branches, each with a terminal pore. 



