ROLLING DOWNS FORMATION (CRETACEOUS) OF CENTRAL QUEENSLAND. 3 



3. Belonostomtis sweeti, sp. nov. 



The state of preservation of the large fossil does not permit any precise estimate 

 of the original proportions of the fish. Jndging, however, hy the analogy of the 

 aUied Brazilian species, the trunk cannot have been less than 0*9 in length, with a 

 maximum depth of 0-14 in the abdominal region ; while the head, with the opercular 

 apparatus, may have added about 0-4, making the total length approximately 1-3. 

 The individual under consideration is thus and by far the largest member of the 

 genus hitherto discovered. 



[a.) Head and Opercular Apparatus. — As shown by the fragment M. 31, the cranium 

 is well ossified in the occipital, otic, and prefrontal regions. The exoccipital extends 

 considerably into the lateral wall of the brain-case, and is bounded in front by a large 

 pro-otic element, separated only by suture, extending downwards to the base of the 

 cranium, and exhibiting near its hinder border a large oval foramen, evidently for the 

 exit of the glosso-pharyngeal nerve. The membrane bones of the cranial roof are 

 thick ; and there is a robust parasphenoid bone, expanding in front of the orbit. The 

 jaws are not preserved, and the only element of the suspensorium exhibited is the 

 hyomandibular, which lies beneath the opercular apparatus of the left side in the 

 large fossil. As usual in Belonostomtis, this bone is lamelliform, with a much 

 expanded, squamous, inferior moiety, and a narrow, more robust, superior portion, 

 from which at the hinder border would arise a short, stout process for the articulation 

 of the operculum. Externally, remains of large suborbital membrane bones 

 (Fig. 1, 50.) are conspicuous between the orbit {orb.), and the preoperculum (p.op.) ; 

 these being ornamented with coarse tuberculations rarely fused into irregular rugte. 

 The preoperculum {p.op.) is a deep triangular bone, tapering, though notably 

 robust, above, and terminating in a truncated expansion below. Its upper extremity 

 reaches a point not far below that of the operculum, and the length of its inferior 

 border exceeds half the height of the bone. The operculum {op.) is approximately 

 quadrate in form, with a somewhat truncated and rounded postero-superior 

 angle. Its maximum depth and breadth are nearly equal ; the upper border 

 is somewhat turned inwards, and the articular pit {a) for the reception of 

 the process from the hyomandibular is especially prominent near the antero- 

 superior angle. The sub-operculum {s.op.) is comparatively small, deepest and 

 truncated in front, gradually tapering to a posterior apex at the postero-inferior angle 

 of the operculum. All these bones are superficially ornamented with prominent 

 tuberculations of ganoine, wliich are partly fused into irregular radiating series, but 

 still more conspicuously arranged in concentric lines. 



{b.) Branchial Apparatus. — As shown by the small fossil M. 26 A, the gill-arches 

 are slender, and shaped like those of modern Teleosteans, being a series of narrow, 



