﻿426 ACTINOPTERTGII. 



bony splints. The maxilla (m.v) is a narrow, elongated element, 

 much expanded behind the eye ; the premaxilla (pmx) is compara- 

 tively small and insignificant. Surrounding the eye is a narrow ring 

 of four thin bones (circumorbitals) bounded behind by others of the 

 " suborbital " series (s.o) ; and the space between the latter, the 

 cranial roof, maxilla, and opercular apparatus is covered by a single 

 bent bone, interpreted by Traquair as preoperculum (p. op). In 

 the mandible the articular portion of the meckelian cartilage is os- 

 sified, and the rest is ensheathed outside by a very large dentary 

 (d) and a small angular (ag), while its inner face is equally covered 

 by an extensive laminar splenial. Both the splenial and dentary, as 

 a rule, bear teeth. The hyomandibular element of the suspensorium 

 is well ossified superficially and is thus usually preserved, but no 

 symplectie has been noticed ; the former is much elongated, and 

 somewhat bent at about the position of the lower border of the 

 operculum. The ptery go-quadrate seems to be ossified at least at the 

 quadrate articulation ; and there is evidently a large, elongated 

 membrane-bone ensheathing its inner or oral aspect. The oper- 

 culum {op) is suspended from the hyomandibular, and is usually 

 narrow, bounded below by a large suboperculum (i.op.), often with 

 indications of a feebly developed interoperculum. Beneath the sub- 

 operculum, the opercular fold is strengthened by a series of lamelli- 

 form branchiostegal rays (hr), which meets the corresponding series 

 of the opposite side in front, and terminates in an anterior azygous 

 element at the symphysial angle of the mandible. The branchial 

 arches are sometimes seen to be ossified. 



In the axial skeleton of the trunk, the notochord must have been 

 persistent, and there is as yet no definite evidence of ossifications in 

 its sheath. The neural arches and spines throughout the trunk, and 

 the haemal arches, with their spines in the caudal region, are super- 

 ficially ossified, and are thus observed when there is no obscuring squa- 

 mation ; but there are no traces of ribs in any genus, the abdominal 

 haemal arches being merely small short pieces of cartilage. In the 

 only genus in which they have been well displayed (Coccolejns), the 

 neural spines are not fused with the supporting arches in the abdom- 

 inal region, but both these and the haemal spines are firmly fixed to 

 their arches in the tail ; at the base of the caudal fin the haemals are 

 much enlarged for the direct support of the dermal rays, while the 

 neurals become gradually aborted, and there is a series of distinct 

 supporting ossicles beneath the fulcra of the upper caudal lobe 1 . 



1 The characters of the axial skeleton are to some extent shown in Ann. Mag. 

 Nat. Hist. [6] vol. v. pi. xvi. figs. 2, 4; but more satisfactory information -will 

 appear in Mem. Geol. Surv. N.S. Wales, Pahsont. no. 9, pis. i.,ii. 



