THE PRIMITIVE DIPNOAN DENTAL PLATE

The study of fossil and extant dipnoan dentitions shows that the shagr een of denticles found in such Devonian genera as Uranolophus and Crip hognathus is not primitive for the group, that the ontogeny of the ext ant Neoceratodus is not a guide to the primitive adult tooth plate, th at homology between teeth on dipnoan tooth plates and polyphyodont mar ginal teeth of other osteichthyans has not been established, and that the Chinese Devonian genus Diabolepis should nor be regarded as a dipn oan. We conclude that no convincing argument has been advanced to dest roy our contention that the primitive dipnoan plate was a relatively f eatureless sheet that was added to at the margins by the incorporation of small enamel-covered dentine blisters, and was thickened by resorp tion of the basal bone and subsequent ingrowth by pleromic dentine.