202 ELOPIFORM FISHES 



features Elopoides may be considered ancestral to either or both of the Eocene 

 megalopids. 



Of the Eocene megalopids, Protarpon and Promegalops, the former is more primitive 

 and resembles Tarpon. Promegalops is closely related to Megalops, the similarities 

 including the shape of the neurocranium and the position of the lower jaw articula- 

 tion. Whether Promegalops is more closely related to Protarpon or Elopoides is 

 unknown, there being no evidence one way or the other. 



(d) Suborder Albuloidei 



The suborder Albuloidei consists of three families, the Albulidae, Pterothrissidae 

 and Osmeroididae (nov.). The suborder is known in the fossil record from the Albian 

 and is represented in the Recent fauna by three genera (Albula, Dixonina and Ptero- 

 thrissus). The Albulidae and Pterothrissidae are very much alike, more so than 

 either is to the stem family, the Osmeroididae, and in the discussion of the families 

 the first two are considered together. The Osmeroididae show few of the specializa- 

 tions of the Albulidae or the Pterothrissidae. 



Fishes grouped here as the Albulidae and Pterothrissidae have been recognized 

 as a distinct assemblage but placed near the elopoid fishes because of the common 

 possession of many primitive features (Ridewood 1904). The Osmeroididae, 

 containing the genus Osmeroides and possibly Dinelops, have in the past been asso- 

 ciated with the Elopidae (Woodward 1901 and all subsequent authors). Although 

 Osmeroides does not show many albuloid specializations, it shares with these fishes 

 a pattern of neurocranial architecture which is significantly more advanced than 

 that of the Elopidae and completely different from that of the Megalopidae. Fur- 

 thermore, within the genus Osmeroides can be seen the initiation of morphological 

 trends that were to become fully expressed in both the Albulidae and the Ptero- 

 thrissidae. In other words, the Osmeroididae are a link between the Elopidae on 

 the one hand and the Albulidae and Pterothrissidae on the other. The Osmeroididae 

 are included in the Albuloidei on the basis of neurocranial specializations. 



In all albuloids the neurocranium is shallow and the subtemporal fossa is deep, 

 extending inwards to partially occlude the post-temporal fossa. The latter is small 

 and directed antero-medially. The sub-epiotic fossae augment the post-temporal 

 fossae in receiving the epaxial trunk musculature. The dilatator fossae are always 

 deep, narrow dorso-ventrally and completely roofed. In the lateral neurocranial 

 wall there is a large ridge running across the face of the prootic which provides a 

 point of attachment for the anterior branchial musculature. The otic bulla, con- 

 taining the sacculith, is very large and precludes any possibility of there being a 

 primitive type of otophysic connection (cf. Megalopidae). There is no prootic- 

 intercalar bridge, indeed the intercalar is reduced in albuloids. The lateral ethmoid 

 and parasphenoid meet, sometimes in a suture. Finally, there is a deep depression 

 at the base of the parasphenoid ascending wing, the significance of which is not known. 



Other advanced cranial characters found in nearly all albuloids are the enlarged 

 sensory canals (developed to varying degrees throughout the group), a reduced 

 supratemporal, resulting in the middle portion of the supratemporal commissure 

 running in the skin, and the position of the quadrate/mandibular articulation which 



