LABYKINTHODONTIA 197 



Labyrinthodon, but with a peculiarly polished ganoid-like 

 surface, from the muschelkalk of Luneville. 



In all the foregoing forms of Labyrinthodonts, represented 

 by complete crania, with the exception perhaps of Zygosaurus, 

 the supplemental osseous plates roofing over the temporal 

 fossad are present, as in Archegosaurus, viz., the " post-orbital " 

 and the " super-squamosal " bones. In all of them the occipital 

 condyles are distinct, forming a pair ; and in all the vomer is 

 divided and bears teeth. The structure and disposition of the 

 entire dental system is strictly labyrinthodont. 



The relation of these remarkable reptiles to the saurian 

 order has been advocated to be one of close and true affinity, 

 chiefiy on the character of the extent of ossification of the, 

 skull, and of the outward sculpturing of the cranial bones. 

 But the true nature of some of these bones appears to have 

 been overlooked, and the glance of research for analogous 

 structures has been too exclusively upward. If directed down- 

 ward from the Labyrinthodonts to the Archegosauri and certain 

 ganoid fishes, it suggests other conclusions. 



The conformity of pattern in the dermal, semidermal, or 

 neurodermal bones of the outwardly well-ossified skull of 

 Polyptcnis, Lcjndosteus, Sturio, and other salamandroid-ganoid 

 fishes, with well-developed lung-like air-bladders, and of the 

 same skull-bones in the Archegosaurus and the Labyrintho- 

 donts ; the persistence of the notochord (chorda dorsalis) in 

 Arcltcgumurus, as in Sturio ; the persistence of the notochord 

 and branchial arches in Archegosaurus, as in Lepidosircn ; the 

 absence of occipital condyle or condyles in Archegosaurus, as 

 in L&pidosiren ; the presence of labyrinthic teeth in ArcJteyu- 

 saurus, as in Lqridosteus and Labyrinthodon ; the large median 

 and lateral throat-plates in Archegosaurus, as in Mcgaliehthys, 

 and in the modern Ara/paima and Lepidosteus; — all these 

 characters point to one great natural group, peculiar for the 

 extensive gradations '>!' development, linking and blending 



