CTENOTHRISSA. 79 



which forms the ventral border of the flank ; all the scales very finely serrated and 

 deeply pectinated, those of the anterior portion of the fish at least also marked with 

 large flattened tubercles. 



Description of Specimens. — The type specimen in the Mantell Collection (no. 

 4029) exhibits the general form of the fish, with the flattened lower face of its 

 abdominal region. It also displays the characters of the squamation. The fossil, 

 however, is too imperfect to show clearly that it does not belong to the Berycidae, 

 and the foremost ray of the pelvic fin might readily be mistaken for a spine, as it 

 is described by Agassiz. The detached head figured by Agassiz (tout, cit, pi. xiv b, 

 fig. 7) evidently shows the toothed Clupeoid maxilla ; but this specimen does 

 not appear to have been received by the British Museum with the Mantell 

 Collection, and it has not hitherto been identified. 



The cranium is short, deep, and narrow, with a relatively small cerebral region. 

 The plane of its roof slopes straight downwards to the sharply pointed snout; 

 while the basicranial axis is bent upwards at the anterior end of the brain-case 

 (B. M. no. 2593G). The greater part of the cranial roof is formed by the frontal 

 bones (PI. XVII, fig. 2 a, fr.), which are somewhat longer than wide. They are 

 widest at the hinder border of the orbit and rapidly taper forwards, where they 

 overlap the very small and narrow mesethmoid (eth.). They are bent on each side 

 into a supraorbital flange, which bears a coarsely rugose or tubercular ornamenta- 

 tion ; they are also traversed by a pair of large longitudinal slime-canals, which 

 bifurcate in front. The parasphenoid bone is stout, and its hinder part forms the 

 floor of a large basicranial canal, seen especially in B. M. no. P. 5685. 



The mandibular suspensorium is inclined forwards, so that the articulation of 

 the mandible is beneath the anterior part of the orbit. The hyomandibular is 

 rather stout, narrow, and deep, with a vertical laminar ridge on its outer face 

 (B. M. no. P. 5418). The quadrate (PI. XVII, fig. 1, qu.) is deeply clef t behind to 

 clasp the symplectic element (B. M. no. 41775). Both the ectopterygoid and 

 entt (pterygoid are thin, toothless lamina?. The premaxilla (PL XVII, fig. 2, pmx., 

 and fig. 2 b) is relatively small, and cannot have formed more than one quarter of 

 the toothed edge of the upper jaw. Its anterior end rises into a large ascending- 

 process, which makes an angle greater than a right-angle with the tooth-bearing 

 portion. Its teeth are very small, blunt cones, arranged in a narrow cluster. The 

 maxilla (PI. XVII, figs. 1, 2, mx., and fig. 3) is a large stout lamina, shaped like 

 that of Clupea. As seen from the inner face (tig. 3), its tooth-bearing portion is 

 nearly four times as long as dee]), truncated at the hinder end, and rising into a 

 very slight prominence at the middle of the upper edge. Its gently curved oral 

 border bears a single series of small and nearly uniform, bluntly conical teeth. 

 The anterior part of the bone is a narrow bar, not quite half as long as the tooth- 

 bearing lamina: it gradually rises to the palatine articulation. The exposed part 

 of the outer face of the maxilla is finely ornamented with rugee, which are mainly 



