HYBODUS. 7 



and produced somewhat forwards at its upper end, antero-posteriorly compressed 

 but less expanded at its lower end. The pterygo-quadrate (as seen especially in 

 PL II, fig-s. 1, 1 a (pfq.), and in the specimen figured in Catal. Foss. Fishes, Brit. 

 Mns., pt. i, pi. xii, fig. 1) is weak and depressed at its anterior symphysis, but 

 deepens rapidly backwards, so that by the middle of the orbit its depth equals at 

 least a quarter of its total length. Its upper border is then slightly concave, and 

 finally rises a little to its highest point behind. It can scarcely have articulated 

 with the postorbital prouiinence of the cranium. The outer face of its posterioi' 

 half is indented below, and this hollow is overhung by an arched ridge which runs 

 upwards and forwards from the articular end and dies out l^efore reaching the 



Fig. 3. — Hybodus basatws, Egertou ; restoration of cranium, iipi>er view (A), and of skull with jaws, 

 right side view (B), about one-half nat. size. — Weald Clay; Povensey Bay, Sussex. 



upper border. The rami of the mandible (PI. I, figs. 1, 1 '^ ; PI. II, figs. 1 (/, 1 b ; 

 ind.), though deep and massive behind, rapidly taper forwards and meet in a 

 comparatively feeble symphysis, Avliich does not extend so far as the front of the 

 upper jaw. There are two pairs of large labial cartilages, best shown in PI. II, 

 figs, la, lb {u.l. 1, 2, l.l. 1, 2). Those of the upper and lower anterior pairs are 

 long and band-like ; those of the upper posterior pair (PI. II, fig. 1 a, u.l. 2) are 

 large, irregular laminge ; while those of the lower posterior pair (PI. II, fig. 1 b, LI. 2) 

 are short but stout rounded rods. An attempted restoration of the skull with jaws 

 is given in Text-fig. 3. 



As shown by the type specimen (PI. I, fig. 1) the teeth are in contact round 

 the margin of the jaws, and at least three or four series, one behind the other, 

 must have been simultaneously in use. An examination of several specimens 



