LABYEINTHODONTIA. 217 



labyrinthic structure. The specimen is from the bunter sand- 

 stone of Soultz-les-Bains. 



Xestorrhytias Perrini. — By this name M. von Meyer would 

 indicate certain flat cranial bones, sculptured like those of 

 Laby rintlwdon, but with a peculiarly polished ganoid-like sur- 

 face, 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 

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

 and the " super-squarnosaF bones. The occipital condyles 

 are distinct, forming a pair ; and the vomer is divided and 

 usually bears teeth. The pattern of the sculpturing, although 

 pitted near the centre of ossification of the cranial bone, 

 soon becomes reticulate and then radiate. The upper surface 

 of the skull is also impressed by wavy (mucous?) canals, 

 symmetrically disposed. 



The relation of these remarkable reptiles to the saurian 

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

 chiefly 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 

 downward 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 Polypterus, Lepidostew, Sturio, and other ganoid fishes, 

 with well-developed lung-like air-bladders, and in the same 

 skull-bones of Archegosaurus and the Labyrinthodonts ; the 

 persistence of the notochord in Archegosaurus, as in Sturio ; 

 the persistence of the notochord and branchial arches 

 in Archegosaurus, as in Lepidosiren ; the absence of occi- 



