Labyrinthodon/rom Warwickshire. 541 



modification of the thorax, which could only be inferred from the structure of the 

 nasal cavity in the larger Labyrinthodons. And the light which the small reptile 

 from the Leamington sandstone thus throws upon the organization of the larger 

 Warwickshire Sauroid Batrachia is the more valuable on account of the corre- 

 spondence of their vertebral characters, and of the proportions of their locomotive 

 extremities. But the decisive evidence of dental structure is still wanting ; nay, 

 more, it may be objected that the Leamington fossil exhibits a character, in the 

 small, bony, dermal sculptured plates, not yet found in the Warwick or Wirtem- 

 berg Labyrinthodons, which seems to remove it from all Batrachia — the naked 

 reptiles, as they are emphatically termed, — and to approximate it to the Loricated 

 order. Unquestionably these scuta form a striking instance of the Crocodilian affi- 

 nities of the Leamington Batrachian ; but we have already seen the same affinities 

 manifested in other parts of their organization, by the Warwick and Wirtemberg 

 Labyrinthodons. As these detached superficial bones are the most liable to be 

 separated from the fragmentary skeleton of the individual they once clothed, the 

 mere negative fact of their absence, when so small a proportion of the bones of the 

 trunk of any Labyrinthodon has yet been found, is insufficient to prove a difference 

 of dermal structure between the Leamington and Warwickshire species. 



No anatomist, indeed, can contemplate the extensive development and bold sculp- 

 turing of the dermal surface of the cranial bones in the Labyrinthodontes pachy- 

 gnathus and leptognathus, without a suspicion that the same character may have 

 been manifested in bony plates of the skin in other parts of the body. And grant- 

 ing that this structure existed, to what extent, it may be asked, does it affect the 

 claims of the Labyrinthodon to be admitted into the order of Batrachia, in which 

 every known species is covered with a soft, lubricous and naked integument ? To 

 this question it may be replied, that the skin is the seat of the most variable characters 

 in all animals ; and, if considered apart from the modifications of the osseous and 

 dental systems, is apt to mislead the naturalist who is in quest of the real affinities of a 

 species. Suppose, for example, that the existing Chelonian reptiles were exclusively 

 mud-tortoises, or with a soft and naked skin, as in the species of Trionyx and Sphargis, 

 would the discovery of the osseous carapace of a true Testudo, in a fossil state, in 

 connexion with a skeleton in other respects essentially corresponding with the modi- 

 fications exhibited by a Trionyx, prohibit the association of the fossil in the same 

 order of reptiles with the Trionyx, because of the indication of the scutes ? It un- 

 questionably ought not to affect such a determination. And so with respect to the 

 Labyrinthodont Batrachia ; if all the species have pushed their affinities to the 

 Crocodilians so far as to have had their trunk defended by bony dermal plates, yet 

 their double occipital condyle, their comparatively simple lower jaw, their largf 



VOL. VI. SECOND SERIES. 4 A 



