FOSSIL AND RECENT 213 



leptocephalus larva, the development of rostral ossicles and the modification of the 

 outermost pectoral fin-ray to form a pectoral splint. The view expressed by Green- 

 wood et al. (1966) that the presence of a leptocephalus larva links the Elopiformes 

 with the Anguilliformes and Notacanthiformes is accepted here. Much work remains 

 to be done on anguilliform relationships, particularly with respect to their being 

 considered elopiform derivatives. Of these three orders the Elopiformes is the most 

 primitive and represents the basal group from which the other two were derived. 



2. Elopiformes are represented in the fossil record and Recent fauna by between 

 fifteen and twenty genera. The fossil record extends back to the Upper Jurassic 

 where the earliest member is Anaethalion vidali, a species which shows certain body 

 proportions seen in the megalopid elopiforms. 



The genus Anaethalion is held to be of considerable interest. In the present state 

 of knowledge only one species, A . vidali, may be referred to the Elopiformes since it 

 shows a pectoral splint, other species being unknown in this respect. The caudal 

 skeletons of some species show a distinct resemblance to Elops while others show 

 certain euteleostean characteristics. It may be of significance that the caudal 

 skeleton of Anaethalion vidali shows laminar bone, as in euteleostean fishes. In- 

 sufficient information concerning the anatomy of the various species referred to 

 Anaethalion renders a taxonomic revision premature. For this reason these species 

 are referred to as the ' Anaethalion generic complex '. 



3. Within the Elopiformes the Elopidae is the most primitive family and is 

 represented by Davichthys gen. nov., Elops and probably some species of Anaethalion. 

 The elopids have remained virtually unchanged since the Upper Jurassic. The 

 only trends noted are reduction in the branching of the cephalic sensory canals, 

 loss of the ventro-lateral projections associated with the dermethmoid and loss of 

 fringing fulcra. 



4. The Megalopidae, represented by Megalops, Tarpon, Promegalops, Protarpon 

 gen. nov., Elopoides, Sedenhorstia and possibly Pachythrissops, were an early deriva- 

 tive of the Elopidae. The chief trends characterizing this family are : the develop- 

 ment of a superior mouth ; an increase in size of the post-temporal fossae ; the 

 development of a unique type of otophysic connection ; reduction of parasphenoid 

 teeth ; and certain minor modifications in the postcranial skeleton. 



5. The suborder Albuloidei is known from the Albian to Recent. The most 

 primitive albuloids are represented by the genus Osmeroides on which the new family 

 Osmeroididae is based. Osmeroides is a link between the Elopidae on the one hand 

 and the Albulidae and Pterothrissidae on the other. Within the genus Osmeroides 

 there is seen the initiation of morphological trends that were to become fully ex- 

 pressed in the Albulidae and Pterothrissidae. Osmeroides lewesiensis is the most 

 primitive species, showing an external morphology very much like that of the elopids. 

 The neurocranium, however, is albuloid in such features as small antero-medially 

 directed post-temporal fossae, sub-epiotic fossae, the absence of a prootic-intercalar 

 bridge, a small intercalar and a deep dilatator fossa. Osmeroides latifrons is a more 

 advanced species and exhibits a slightly elongated snout, opening out of the 

 cephalic sensory canals, specialization of the dentition within the mouth and a 

 short lower jaw with a strongly inflected ventral margin. 



