CESTRACION. 215 



jaws, whicli are naturally associated with the vertebral column and dorsal fin- 

 spines. There is also another example of the jaws with teeth in the British 

 Museum. 



The cartilages are calcified as usual in one superficial layer of compacted poly- 

 gonal tesserffi. The pterygo-quadrate or upper jaw (PL XLV, fig. 1, 2)fq.) 

 projects slightly in front of the mandible, but is not sufficiently well preserved to 

 show whether or not its anterior part articulated with the cranium. The mandible 

 (md.) displays its short symphysis in two specimens. In the anterior cuspidate 

 teeth the crown is smooth on both faces, and there is a single pair of lateral 

 denticles which varies in prominence. The crown overhangs the root on all sides, 

 and its base-line on the outer face is arched (fig. 1 a). The short depressed root is 

 triangular in shape, and its inner apex is pierced by a large nutritive foramen 

 (fig. 2 (i). The transition from these cuspidate teeth to the principal lateral teeth 

 has not been clearly observed, but the latter are well shown in both the specimens 

 already referred to. In the upper jaw of the fossil from the Willett Collection 

 there are parts of three transverse series gradually increasing in size backwards (fig. 

 1 b) ; while in the same jaw of the British Museum fossil the second and third of 

 these transverse series are followed behind by another series (fig. 2 h). There are 

 thus four series of large elongated lateral teeth. They have rounded rather than 

 truncated or bevelled ends. Their crown overhangs the depressed root on all 

 sides and is traversed by a sharp longitudinal keel, whicli is raised into a median 

 eminence. In the conspicuous reticulation of the coronal surface the main lines 

 diverge from this central keel (fig. 1 c). The root is smooth on its inner face, and 

 is often pierced by the oblique canal already described by Egerton (fig. 2 c), In 

 the Willett fossil the teeth of the three series measure respectively 0*5 cm., 0"6 cm., 

 and 0"75 cm. in length; while in the British Museum fossil the measurements are 

 0'5 cm., 0*65 cm., and 0'5 cm. respectively. Some detached teeth in the latter 

 (fig, 2 d), measuring 0'4 cm. in length, probably correspond with those of the first 

 series in the former specimen. There is no evidence of posterior small teeth in 

 either specimen ; but a displaced crushing tooth in front of the principal lateral 

 teeth in the second measures only O'o cm. in length (fig. 2 h, x.). It may belong to 

 the lower jaw. 



The imperfect fish described by Egerton (1872) proves that the fossil drawn 

 in PI. XLV, fig. 3, represents part of the vertebral column with the anterior 

 dorsal fin-spine of this species. The vertebral centra are shown to be astero- 

 spondylic, with few stout radiating plates ; and a little behind the fin-spine they 

 begin to be comparatively short and deep. Though imperfect in the middle, the 

 fin-spine is not broken across and so exhibits its precise shape. It is hollow 

 and much laterally compressed, with a deep base of insertion, and its exposed 

 portion is covered with a smooth layer of ganoine. Its posterior border is 

 longitudinally channelled, but without denticles. As already noted by Egerton, 



