92 FOSSIL FISHES OF THE ENGLISH CHALK. 



gradually lengthening slender rays appear outside the basal half of its longest ray 

 above and below ; while this and the other outermost rays, not far from their base, 

 exhibit numerous closely arranged, oblique articulations, each in the form of a 

 finely jagged line (PL XX, fig. 2 a). 



The scales are large, very deeply overlapping, smooth, and not serrated or 

 crenulated on the posterior margin. When the outermost layer is partly destroyed, 

 they exhibit a few very fine, parallel or slightly radiating lines directed antero- 

 posteriorly in the exposed area. It is impossible to count them accurately, but as 

 suggested by the type specimen there seem to have been 12 scales in a transverse 

 series on the flank of the abdominal region, and there are 8 or 10 of these series 

 in front of the dorsal fin. One scale, of ordinary shape, behind the upper end of 

 the pectoral arch (PI. XX, fig. 2, x.), is strongly marked with radiating furrows, 

 which were evidently in connection with a sensory canal. The lateral line 

 (PI. XX, fig. 1, //.) is prominent as a simple tube piercing all the scales it traverses. 

 It begins in front low down on the flank, not far above the pectoral fin, and rises 

 slightly as it is traced backwards to the middle of the fish. 



Horizons and Localities. — Turonian zones : neighbourhood of Burham, Cuxton, 

 and Dunton Green, Kent. Zone of Holastcr subglobosus : Burham and Dover, 

 Kent ; Glynde, Sussex. Undetermined zones : Guildford and Shalford, Surrey. 



Family Chirocenteid^. 



The sole surviving member of this family, Chirocentrus dorab (Text-fig. 21) of 

 the Indian Ocean, is interesting as having the intestine short, with a rudiment of 

 the spiral valve, which is so characteristic of the ganoid fishes. The Cretaceous 



Fig. 21. — Chirocentrus dorab, Forsk. ; about one seventh nat. size. — Existing in the Indian Ocean, Chinese, 



and Japanese Seas. 



genera here referred to the Chirocentridre exhibit a skeleton essentially identical 

 with that of Chirocentrus, differing only from the latter by the implantation of the 

 teeth in deep sockets, and by two features on the side of the skull. Jrhtlnjodectes 

 and r<>rlhrus at least lack the small vacuities in the base of the outer side of the 



