98 



NEW YORK STATE MUSEUM 



fact in considering;' the relations between fossil and recent forms. It has 

 been shown by Semon' that the dental plates of the modern genus arise 

 through concresence of conical denticles, which are at first disposed so as 

 to form two pairs of palato-pter)'g-oid plates, these afterwards fusing into 

 one ; and, thanks to this observation, we can readily account for what would 

 appear at first sight to be a supernumerary pair in Mylostoma. Moreover, 

 it will be noted that the peculiar posterior contour of the hindermost pair 

 of plates in the fossil form is scarcely to be explained except as we regard 

 it in association with, and conformable to, the usual pattern of palato- 

 pterygoid cartilage found in all Dipnoans. Amongst Ctenodipterines this 



Fig. t8 Mylostoma v a r i a b U c Ncwljerry. Cleveland Khale ; Sheffield, O, Palato-pterygoid dental plates, arranged 

 ill nalurul position, but beb:inging to difterent individuals. The vomerine pair is supposed to have been situated imme- 

 diately in front, but no specimens undoubtedly assignable to this position are at present known, x -J 



element is ossified, and passes under the name of "upper dentigerous 



bone," yet it preserves essentially similar outlines, and bears the stamp of a 



persistent feature. 



The mandibles of Mylostoma betray unmistakable traces of a Cerato- 



dont origin, for the dental plate properly speaking is even more sharply 



distinguished from the splenial than in Dinichthys or Dinomylostoma. The 



presence of intermandibular teeth would be in complete harmony with 



embryological evidence, and as a matter of fact certain detached teeth have 



".Semon, R. ])ie Zahnentwickehing de.s Ceratodus forsteri. Zool. Forschungsreisen 

 in .■\iistrjlien etc. Jena Denksclir. 1901. 4: 11 S~33. 



