28 4 



HISTORICAL PALEONTOLOGY. 



central cone, flanked by minor lateral cones ; and the fin- 

 spines (fig. 207) are longitudinally grooved, and carry a series 

 of small spines on their hinder or concave margin. Lastly, 

 the great modern order of the Bony Fishes or Teleosteans 



Fig.'206. Tooth 

 of Hybodus. 



Fig. 207. Fin-spine of Hybodus. Lower Greensand. 



makes its first appearance in the Upper Cretaceous rocks, 

 where it is represented by forms belonging to no less than 

 three existing groups namely, the Salmon family (Sal- 

 monidce), the Herring family (Clupeidce), and the Perch family 

 (Percida). All these fishes have thin, horny, overlapping 

 scales, symmetrical (" homocercal ") tails, and bony skeletons. 



Fig. 208. 1, Keryx Lewesiensis, a Percoid fish from the Chalk ; 2, Oameroides 

 Mantelli, a Salmonoid fish from the Chalk. 



The genus Beryx (fig. 208, i) is one represented by existing 

 species at the present day, and belongs to the Perch family. 



