8o ELOPIFORM FISHES 



the operculum is smoothly rounded, without the characteristic indentation seen in 

 Tarpon and Megalops. 



In all of the above respects Protarpon is more primitive than the Recent mega- 

 lopids. It shows no specialization that would exclude it from being an ancestor to 

 either or both of the Recent genera. The apparent greater similarity to Tarpon 

 rather than Megalops can be attributed to the relative primitive nature of Protarpon 

 and Tarpon. These two last genera share such characters as a relatively shallow 

 neurocranium, with the maximum depth at the occiput, a straight parasphenoid, the 

 primitive position of the jugular foramen and the lack of a bony covering to the 

 swimbladder/ear connection. 



Genus PROMEGALOPS Casier, 1966 



1966 Promegalops Casier : 120. 



Diagnosis (emended) . Megalopid fishes in which the neurocranial roof is markedly 

 convex above the cranial vault. Parietals slightly longer than broad. Dilatator 

 fossa shallow, partially roofed by a very thin ledge formed by the pterotic and auto- 

 sphenotic. Maximum depth of the neurocranium at the level of the autosphenotic. 

 Parasphenoid bent at the level of the ascending wings. Mandible shallow, coronoid 

 process weakly developed. Operculum with antero-dorsal indentation. 



Type-species. Promegalops signeuxae Casier, 1966. 



Promegalops sheppeyensis Casier, 1966 

 (Text-figs. 41-43) 



Remarks. Casier (1966) erected the genus Promegalops for two specimens from 

 the London Clay (Ypresian) of Sheppey, Kent, England. For each specimen a new 

 species was erected, P. signeuxae (the type-species) and P. sheppeyensis (for a speci- 

 men formerly included in Megalops prisons, B.M.N.H. P. 9192). The former is 

 known by a nearly complete head, the latter from a neurocranium. Both have 

 been adequately described by Casier (1966), but apart from referring the genus to 

 the Elopidae (including the Megalopidae) he came to no definite conclusions about 

 the affinity of this genus. 



The megalopid nature of Promegalops is shown by the deep skull with a lower jaw 

 which is obliquely inclined towards the snout ; a dentary symphysis which protrudes 

 slightly ; the otic region of the neurocranium which is short and deep ; and by the 

 dermethmoid and mesethmoid which have a similar shape to that seen in Recent 

 megalopids (Casier 1966 doubts the presence of the postero-ventral projection of the 

 ethmoid which occurs in the Recent species) . 



Promegalops differs from the contemporaneous Protarpon in the following important 

 respects : skull roof markedly convex above the cranial vault ; autosphenotic spine 

 moderately well developed ; dilatator fossa shallow and partially roofed by a very 

 thin ledge of the pterotic and autosphenotic ; neurocranium deep, with the maximum 

 depth at the level of the autosphenotic ; parasphenoid bent beneath the level of 



