1894.] SALMONOID FISHES OE THE ENGLISH CHALK. 661 



The cheek-plates are large, but comparatively thin ; and the only- 

 evidence of ornament consists in radiating lines on the large postero- 

 inferior suborbital (B.M. nos. 49903, P. 5681). The maxilla is 

 very robust and arched so that the oral margin is convex (fig. 4, 

 mx.). Anteriorly it is produced upwards and inwards as a long 

 narrow process (p.) above the premaxilla towards its attachment in 

 the front of the ethmoidal region ; the upper portion is a thin 

 lamina overlapped by two supramaxillary plates (figs. 3 «, 4, s.mx.), 

 of which the liindermost is deepest and has an anteriorly directed 

 process at its front upper angle. The premaxilla (fig. 4, pmx.) is 

 shown to have been moderately extended beneath the maxilla. 

 The mandible is deepest in the coronoid region, and the angular 

 element (tig. 2 a, ag.) is very large, extending for a length of more 

 than two-thirds that of the dentary (d.) on the outer surface. The 

 inferior border of the ramus is slightly bent inwards, and along the 

 angle thus formed the sensory canal opens in a longitudinal series 

 of small pits (fig. 5). The teeth are very minute and clustered on 

 the margin of both jaws. 



Behind the occipital on each side there is a small sv/pratemporal 

 plate, and partly covered by this is a large post-temporal element. 

 The opercidum (fig. 5, op.) is trapezoidal in form, nearly twice as 

 deep in front as behind. The suboperadum {s.op.) is somewhat less 

 than half as deep as the latter, and has a prominent ascending 

 process at its antero-superior angle. The preopereidum (fig. 4, p.op.) 

 is well exposed, with the inferior limb sharply bent forwards ; and 

 its outer face is marked by a sharp vertical ridge giving rise to a 

 few radiations at the angle. The interopercidmn (fig. 5, i.op.) is 

 long and narrow, and the hrancJiiostegal rays, shown to the number 

 of eight or nine in fig. 5 (6r.), are broad. It is also interesting to 

 observe that between the rami of the mandible (fig. 5, d.) there is 

 a long narrow azygous gidar plate (gu.), quite smooth on the outer 

 face and regularly rounded at each end. 



One specimen (no. 47932) exhibits at the back of the head 

 remains of a close series of small styliform bones, acutely pointed 

 at the anterior end, attached by a slight expansion at the hinder 

 end. These are probably gill-raJcers. 



The vertebral centra are robust and the secondary lateral ossifi- 

 cations are in the form of delicate longitudinal ridges. Appear- 

 ances in nos. 49903 and P. 4247 suggest that there was a perfora- 

 tion in the middle of each centrum allowing for the passage of a 

 persistent thread of notochord ; while it is clear that the neural 

 arches throughout and the hasmal arches in the caudal region are 

 fused with the supporting centra. Bibs also are seen in the 

 abdominal region, not extending quite to the ventral border. The 

 number of vertebras cannot be counted, but there seem to have been 

 not less than twenty in the abdominal region. The anterior 

 abdominal vertebral centra are deeper than long — those most 

 posteriorly at least as long as deep. 



The pectoral arch is obscure, but the remains, shown from the 

 inner aspect in fig. 6, exhibit the relatively large elongated supra- 



