GANOIDEI. 



359 



may, infer that the young are provided with external gills, as 

 in Protopterus and Polypterus. 



The discovery of Ceratodus does not date farther back 

 than the year 1870, and proved to be of the greatest iaterest, 

 not only on account of the relation of this creature to the other 





Fig. 140. — Tooth of fossil Oeraiodus from Aust, near Bristol, natural size. 



living Dipnoi and Ganoidei, but also because it threw fresh 

 light on those singular fossil teeth which are found in strata 

 of Triassic and Jurassic formations in various parts of Europe, 

 India, and America. These teeth, of which there is a great 

 variety with regard to general shape and size, are sometimes 

 two inches long, much longer than broad, depressed, with 

 a flat or slightly undulated, always punctated crown, with 

 one margiu convex, and with from three to seven prongs pro- 

 jecting on the opposite margin. 



Second Family — Ctenododipteeid^. 



Caudal Jin Jieterocercal. Gular plates. Scales cycloid. Two 

 pairs of molars and one pair of vomerine teeth. 



p 



Fig. 141. — Dipterus macrolepidotus. 



Extinct. Dipterus (Otenodus), Eeliodus from Devonian strata. 



