TOMOGNATHUS. 139 



Genus TOMOGNATHUS, Dixon. 

 Tomognathus, F. Dixon, Geol. Sussex, 1850, p. 376. 



Generic Characters. — Head short and deep, much laterally compressed, with a 

 thin supraoccipital crest extending along half its length ; the orbit very large and 

 far forwards ; no cheek-plates. Cleft of mouth horizontal ; dentigerous half of 

 mandible slender, its hinder half deepened ; teeth hollow and conical, enamelled 

 only in their distal half, arranged in a close series, not in sockets but directly fused 

 with the jaw ; premaxillary and anterior dentary teeth the largest ; a series of 

 small teeth on the ectopterygoid, and another very small series within the con- 

 spicuous row of mandibular teeth. 



Type Species. — Tomognathus mordaoc, from the English Chalk. 



1. Tomognathus mordax, Dixon. Plate XXIX, figs. 3 — 13. 



1850. Tomognathus mordax, F. Dixon, Geol. Sussex, p. 376, pi. xxxv, fig. 1. 



1850. Tomognathus leiodus, F. Dixon, op. cit., p. 377, pi. xxx, fig. 31. [Mandibular ramus : British 



Museum.] 

 1888. Tomognathus mordax, A. S. Woodward, Proc. Geol. Assoc, vol. x, p. 313. 

 1901. Tomognathus mordax, A. S. Woodward, Catal. Foss. Fishes B. M., pt. iv, p. 117. 



Type. — Imperfect skull, with jaws. 



Specific Characters. — The type and only known species, the head with opercular 

 apparatus attaining a length of 7 cm. Orbit occupying nearly half the total length 

 of the head, the maxilla nearly three and a half times as long as its maximum 

 depth, and the mandibular ramus a little more than three times as long as its 

 maximum depth. The robust premaxillse fused together, and each bearing four 

 large teeth gradually decreasing in size from the middle line to the side ; these 

 teeth scarcely tumid at the base, nearly straight, enamelled and faintly fluted in 

 their distal half. None of the maxillary teeth more than half as large as the 

 latter, very slender, and rapidly becoming small in the very close series behind ; 

 about eight teeth in the ectopterygoid series as large as the anterior maxillary 

 teeth. Outer mandibular teeth closely similar to those of the premaxilla, but 

 those at the symphysis a little more tumid at the base and incurved at the apex ; 

 the foremost tooth relatively small, the next three the largest, then another small 

 one as the first of a diminishing series of about six to eight teeth. Width of 

 operculum nearly equalling one quarter the length of the skull; suboperculum 

 wider than deep ; both destitute of superficial ornament. 



Description of Specimens. — The type specimen appears to have been lost, but 

 Dixon's figure shows the characteristic jaws and teeth, with the anterior half of 



