GANOIDEI. 



359 



may infer thai the young are provided witli external gills, as 

 in Protopterus and Polypterus. 



The discovery of Ccratodus does not date fartlier back 

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

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



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



living Dipnoi and Ganoidei, but also because it threw fresh 

 light on those singular fossil teeth wiiich 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 margin convex, and with from three to seven prongs pro- 

 jecting on the opposite margin. 



Second Family — Ctenododipteridj]:. 



Caudal fin heterocercal. Gidar 2)lates. Scales cycloid. Tvjo 

 pairs of molars and one 2'>air of vomerine teeth. 



Fig. 141. — Dipterus macrolepidotiis. 



Extinct. Lipterns {Ctcnodus), Hcliodus from Devonian strata. 



