FOSSIL AND RECENT 9 



Much of the cranial roof is formed by the paired frontals. Each frontal is narrow 

 anteriorly but widens at the level of the lateral ethmoid and again above the auto- 

 sphenotic spine. Above the orbit the lateral margins of the frontals are parallel, 

 a resemblance to leptolepids rather than pholidophorids. Posteriorly each frontal 

 ends squarely, with a slight overlap above the parietal and pterotic of its side. The 

 mutual interfrontal suture is straight in young individuals, where there may be a 

 divergence of the bones anteriorly exposing the ethmoid cartilage. In the adult, 

 however, the frontals meet one another throughout their length and the suture line 

 becomes wavy posteriorly. Ornamentation upon the frontal is confined to the ridges 

 associated with the sensory canals and is described below. 



The anterior end of the cranial roof is formed by the median dermethmoid (rostral 

 of Gardiner 1963 and Nybelin 1956, 1967a). The dermethmoid is long, unlike that 

 bone in pholidophorids and Liassic leptolepids, and overlaps the frontals, a fact 

 which reinforces its interpretation as a dermal element. The ethmoid commissure 

 runs transversely across the dermethmoid at the level of the maximum width of the 

 latter element. The commissure, which is relatively large in young individuals, 

 is contained within a bony tube perforated dorsally by two pores. In young in- 

 dividuals this bony tube appears to be an ossification distinct from the underlying 

 dermethmoid but in older individuals it appears as an integral part of that bone. 



The nasals, although not strictly part of the neurocranium, may be considered 

 here as they are closely associated with the roofing bones. Each nasal is tube-like, 

 barely larger than the sensory canal that it carries. The nasal is pierced dorsally by 

 four large pores. Gosline (1965) reported the presence of a small prenasal ossicle 

 in Elops saurus, which according to Nybelin (1967a) may become incorporated in 

 the lateral rostral ossicle. I have found no such prenasal in E. hawaiensis. How- 

 ever, the possibility of there being a prenasal ossicle in some species of Elops is 

 interesting since it may be indicative of a trend among elopiform teleosts, that is, a 

 general tendency toward fragmentation of the dermal bones of the snout. 



The parietal is rectangular and meets its partner in the mid-line except posteriorly 

 where the supraoccipital intervenes for a very short distance. There are recognizable 

 differences in the dimensions of the exposed part of the parietal between young and 

 old individuals. In the young the length of each parietal exceeds its width whereas 

 in the adult the converse is true. The change in shape is due to two factors : 

 differential growth of the parietal in which lateral growth proceeds at a greater 

 rate than longitudinal growth, and secondly the frontals overlap the parietals 

 to a greater extent in older fish. Ornamentation upon the parietals, like that of 

 other cranial bones, is restricted to ridges associated with the sensory canals. 



The postero-lateral region of the neurocranial roof is formed by the dermal portion 

 of the pterotic. The dermal portion of the pterotic forms much of the roof of the 

 post-temporal fossa. The lateral and posterior faces of the pterotic are formed by 

 the thicker but less dense endochondral bone. As is usual among teleosts there is 

 no clear demarcation between the dermal and endochondral portions of the pterotic 

 (Gosline 1969 reports the presence of separate autopterotic and dermopterotic in 

 Alepocephalus) . The lateral face of the pterotic forms the posterior region of the 

 dilatator fossa, much of the hyomandibular facet and the roof of the deep 



