The discovery of Ceratodus does not date farther 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 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 margin convex, and with from three to seven prongs projecting on the opposite margin.
Fig. 141.—Dipterus macrolepidotus.
Second Family—Ctenododipteridæ.
Caudal fin heterocercal. Gular plates. Scales cycloid. Two pairs of molars and one pair of vomerine teeth.
Extinct. Dipterus (Ctenodus), Heliodus from Devonian strata.
Third Family—Phaneropleuridæ.
Caudal fin diphycercal; vertical fin continuous. Gular plates. Scales cycloid. Jaws with a series of minute conical teeth on the margin.
Extinct. Phaneropleuron from Devonian formations, and the carboniferous Uronemus are probably generically identical.