FOSSIL AND RECENT 185 



The cleithrum is large, much of its area being given over to muscle attachment. 

 There are at least 10 pectoral fin-rays. The pelvic fin shows 11 rays. 



The vertebral column is composed of approximately 64 vertebrae, of which 24 are 

 caudal. Over most of the column the neural arches and spines, haemal arches 

 and spines and the parapophyses and ribs are precisely the same as in L. gracilis. 

 Differences occur in those preural vertebrae associated with the caudal fin-rays. 

 Epineural and epipleural (ventral) intermusculars are present throughout the column. 

 There are 22-23 supraneurals, more than in L. gracilis, and this reflects a difference 

 in the position of the dorsal fin which in L. lewisi is situated nearer to the caudal 

 peduncle than to the occiput. The dorsal fin contains 18 or 19 rays. B.M.N.H. 

 P. 4868 shows 10 anal pterygiophores indicating that the anal fin was composed of 

 approximately 12 fin-rays ; B.M.N.H. P. 6024, however, has 7 pterygiophores and 



9 ra ys- 



The caudal skeleton of L. lewisi (Text-fig. 92) is more like that of Albula than is 

 that of L. gracilis. In L. lewisi the supporting neural and haemal spines are expanded 

 antero-posteriorly, there are two epurals and both uroneurals are stout and disposed 

 in typical albuloid fashion. The proximal end of the first uroneural is expanded. 

 This is similar to L. gracilis but unlike Albula vidpes. As is usual in albulids, the 

 neural spine on the second preural centrum is full length. 



What is known about the skull of L. lewisi suggests that it is more primitive than 

 that of L. gracilis. The jaws are relatively longer and less specialized, and the 

 dentition borne by the dermal jaws, palate and basibranchial elements is also more 

 primitive. The caudal skeleton, however, appears more specialized than that of 

 L. gracilis, approaching the Albula condition. 



IV. DISCUSSION OF THE ORDER ELOPIFORMES 



(a) Historical 



With the exception of the pterothrissids, the fishes grouped here as the order 

 Elopiformes have been referred to the families Elopidae and Albulidae by Woodward 

 (1901), Boulenger (1910), Barnard (1925) and Fowler (1936). Pterothrissus (Bathy- 

 thrissa), on which the family Pterothrissidae is based, has been associated with the 

 Salmonidae by Gunther (1877), and the Clupeidae by Gill (1893). A suggestion by 

 Boulenger that Pterothrissus is closely related to Albula was confirmed by Ridewood 

 (1904) who placed the genus in the Albulidae. This author also endorsed Wood- 

 ward's view (1901) that the Cretaceous Istieus is closely related to Pterothrissus. 

 Since that time Istieus and Pterothrissus have been considered as constituting a 

 separate family, closely related to the Albulidae (Berg 1940) or as a subfamily of the 

 Albulidae (Norman i960) or as members of the family Albulidae (Boulenger 1910). 



The fishes grouped in the Elopidae by Woodward (1901) and others have often 

 been divided into two families, the Elopidae and the Megalopidae, which in turn 

 were grouped as a higher taxon of equal rank with that containing the Albulidae 

 and Pterothrissidae (Berg 1940 ; Jordan 1923). Little indication, other than text 



