GANOIDEI. 



369 



The dorsal is opposite to the anal, and all 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 — Aspidorhynchid^, 



Body elongate, with ganoid scales ; jaios prolonged into a 

 heak ; termination of the vertebral column homocercal. Fins 

 loith fulcra ; a series of enlarged scales along the side of the hody. 

 Dorsal fin opposite to the anal. 



Fig. 146. — AspidorhjTichus fisheri, from the Purbeck beds ; m, inaudible ; 

 a, presyniphyseal 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. 



Slxth Family — Pal^oniscid.^. 



Body fusiform, tvith rhomhic ganoid scales. Notochord 

 persistent, tvith the vertebral arches ossified. Heterocercal. All 

 the fins tvith fulcra ; dorsal short. Branchiostegals numerous, 

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

 or cyliTidrical. 



Extinct. Many genera are known; from the Old Eed 



2b 



