i 5 2 ELOPIFORM FISHES 



Except for the lower number of epurals and possibly the differentiation in tooth 

 size, Istieus is the more primitive of the two genera. Both these features may not 

 necessarily be of generic significance because the lower jaw dentition and the caudal 

 skeleton of I. macrocephalus and I. lebanonensis are poorly known. 



Apart from the differences mentioned above there are morphometric and meristic 

 dissimilarities, but there appears to be as much intrageneric variation within 

 Istieus as there are intergeneric differences between it and Pterothrissus. 



The minor differences between Istieus and Pterothrissus are far outweighed by 

 the many important features of similarity in neurocranial anatomy, the hyopalatine 

 series, the infraorbital series, the dermal jaws, the form of the teeth, the cephalic 

 sensory canal system and the fins (particularly details of the caudal skeleton). 



The great similarity in form leads one to ask whether it would be advisable to 

 regard Istieus and Pterothrissus as congeneric. Such a question can only be answered 

 subjectively. Considered alone, none of the differences mentioned above would 

 separate these forms at the generic level, but the nature and sum of the differences 

 lead me to suppose that Istieus is markedly more primitive, to a degree that can only 

 be appreciated by conferring generic status on the Cretaceous forms. 



Genus HAJULIA Woodward, 1942 

 1942 Hajulia Woodward : 557. 

 Diagnosis. See Woodward (op. cit.). 

 Type and only species. Hajulia multidens Woodward. 



Hajulia multidens Woodward 



1942 Hajulia multidens Woodward : 557, pi. 6, fig. 3. 

 Diagnosis. See Woodward (op. cit.). 



Holotype. Nearly complete fish, no. 100509 in the American University, 

 Beirut, from the Middle Cenomanian of Hajula, Lebanon. 



Remarks. Hajulia, from the Middle Cenomanian of Hajula, was considered an 

 albuloid by Woodward (1942) who suggested a relationship with Istieus. 



The pterothrissid nature of Hajulia is indicated by the following features : the 

 rounded trunk as evidenced by the presence of short, curved pleural ribs ; the shallow 

 neurocranium which exhibits a slightly elongated snout ; the mouth which is slightly 

 inferior, and the toothed maxilla which bears a single supramaxilla ; the palatal 

 dentition in the form of large conical teeth on the parasphenoid, endopterygoid and 

 possibly the basibranchium. The coronoid process is placed posteriorly, as in 

 Istieus, and the quadrate/mandibular articulation lies beneath the posterior half of 

 the orbit. There are less than 10 branchiostegals, although the exact number is 

 not known. 



Between the occiput and the dorsal fin there is a complete series of slender supra- 

 neurals. The dorsal fin itself is slightly elongated, situated in the centre of the back, 

 and in profile resembles that of Istieus and Pterothrissus. 



