GANOIBEI. 



369 



The dorsal is opposite to the anal, and aU the fins are pro- 

 vided with a double row of fulcra. This genus ranges from 

 the Lias to the Chalk; one species would seem to have 

 survived into tertiary times, if it should not prove to be a 

 Lepidosteus. 



Fifth Family — AspidoehynchidjE. 



Body elongate, with ganoid scales ; jaws prolonged into a 

 heaJc ; termination of the vertebral coluri^n homocercal. Fins 

 with fulcra ; a series of enlarged scales aj,png the side of the iody. 

 Dorsal Jin opposite to the anal. 



Fig. 146. — Aspidorhjmchus fisheri, from the Purbeck beds ; m, mandible ; 

 a, presympliyseal bone. 



Extinct ; mesozoic. Aspidorhynchus has the upper jaw 

 longer than the lower ; very peculiar is the occurrence of a 

 single, solid, conical bone, situated in front of the symphysis 

 of the lower jaw, to which it is joined by a suture. Belo- 

 nostomus with both jaws of equal length. 



Sixth Family— Pal^eonisoid^. 



Body fusiform, with rhombic ganoid scales. JVotochord 

 persistent, with the vertebral arches ossified. Heterocercal. All 

 the fins with fulcra ; dorsal short. Branchiostegals numerous, 

 the foremost pair forming broad gulars. Teeth small, conical, 

 or cylindrical. 



Extinct. Many genera are known; from the Old Eed 



2b 



