Actinopterygii Percomorphi. 



117 



Tricbiuridao, is that of the Palaeorhynchidse. These are long, 

 slender, laterally-compressed fishes, with a very delicate 

 skeleton, and having the jaws prolonged into a sharply-pointed 

 beak, either edentulous or provided with very small teeth. The 

 dorsal fin is supported by spinous rays and extends along the 

 entire length of the back, and the caudal fin is deeply forked. 



Wall-case, { 

 No. 17. 



FIG. 162. Semiophm'us velicanx, Agassiz, from the Eocene formation of Monte Bolca. 

 A, anal fin ; c, caudal ; D, dorsal ; r, pectoral ; v, pelvic fins. 



In PalceorJiynchum the jaws are of equal length, and an extensive 

 series of specimens is shown in the Wall-case, from the Eocene 

 Slates of Canton Glaris. HemirhyncHus, which has the upper 

 jaw much longer than the lower, occurs both in the Glaris beds 

 and in the Lower Tertiaries of France and Belgium. 



