FOSSIL AND RECENT 125 



Description. Neurocranium. The neurocranium is shown in dorsal, lateral, 

 ventral and posterior views in Text-figs. 60, 61, 62 and 63. It is long and shallow 

 with a slightly elongated snout which is turned downwards at its tip imparting to the 

 head a characteristic albuloid appearance. Cartilage forms much of the ethmoid and 

 nasal capsules and occupies large interspaces between certain bones in the otic region. 



The ethmoid consists of a median vertical plate of cartilage which expands an- 

 teriorly to meet the contours of the dermethmoid above and the vomer below. Along 

 the dorsal surface of the ethmoid there is a thin layer of perichondral bone. Dorsally 

 this mesethmoid is overlain by a large dermethmoid, an element formed by a 

 horizontal plate with a prominent vertical ridge on the dorsal surface. The ridge is 

 pierced by a large fenestra, while anteriorly inclined struts link the vertical ridge 

 with the horizontal portion. Beneath each strut there is an articular facet receiving 

 the head of the premaxilla. The facet is formed by the perichondral mesethmoid. 



The vomer is edentulous and narrow, unlike that element in albulids and os- 

 meroidids. Anteriorly the head of the vomer is slightly expanded and is not clearly 

 separable from the mesethmoid. The head of the vomer is produced ventrally as 

 a stout median ridge which is semicircular in lateral view. 



Each lateral ethmoid is represented by thin perichondral bone which covers the 

 posterior and part of the lateral wall of the nasal capsule. Laterally the lateral 

 ethmoid bears a stout ridge which receives ligaments from the posterior process of the 

 palatine. A single foramen in the transverse wall of the lateral ethmoid transmits 

 the olfactory tract, nasal artery and the superficial ophthalmic branches of V and 

 VII. The lateral ethmoid is separated from its fellow by a narrow strip of ethmoid 

 cartilage. 



The frontal is narrow anteriorly where it is raised in the mid-line to form a ridge 

 lying in continuity with the ridge on the dermethmoid. Above the orbit the lateral 

 margin of the frontal forms a structure resembling a mudguard. Medial to this 

 ' mudguard ' there is a shallow trough which ends posteriorly in a large sensory pore. 

 The nasal lies above the anterior end of the frontal and the posterior region of the 

 dermethmoid. Each nasal is formed by an anterior and larger posterior ossicle, 

 each barely larger than the contained sensory canal. Both ossicles are open dorsally 

 along their entire length. The presence of two ossicles composing the nasal element 

 is noted elsewhere among elopiforms (Elops, Megalops and Tarpon) and is a reflection 

 of a general elopiform tendency towards fragmentation of the snout elements. 



The rectangular parietal is longer than broad and meets its partner over much 

 of its length. A rebate developed along the posterior margin of the parietal contains 

 the central portion of the supratemporal commissure. The parietal is perforated 

 by several small pores (Text-fig. 60) and although the precise disposition of these 

 pores varies from specimen to specimen there appears to be a longitudinal and a 

 transverse series. Such an arrangement of pores is similar to those within the 

 anterior and middle pit-lines of halecostomes, but in the latter fishes the pores are 

 linked by shallow grooves, not seen in Pterothrissus. 



The dermal portion of the pterotic forms the dorso-lateral corner of the skull roof. 

 The otic sensory canal ran within a shallow groove along the lateral edge of the 

 pterotic. A narrow rebate along the posterior margin of the pterotic, which lies 



