402 Geological Society. 



arch, and its chief peculiarity is the expansion of its elongated sum- 

 mit into a horizontally flattened plate, sculptured irrregularly on the 

 upper surface. A similar flattening of the summit of the elongated 

 spine is exhibited in the large atlas of the toad. The body of the 

 vertebrae agrees with that of the L. leptognathus . The humerus 

 is an inch long, regularly convex at the proximal extremity, and 

 expanded at both extremities, but contracted in the middle. A 

 portion of a somewhat shorter and flatter bone is bent at a sub- 

 acute angle with the distal extremity, and resembles most nearly 

 the anchylosed radius and ulna of the Batrachia. 



The femur wants both the extremities ; its shaft is subtrihedral 

 and slightly bent, and its walls are thin and compact, including a 

 large medullary cavity. The tibia? are as long, but thicker and 

 stronger than the femur. They had lost their articular extremities, 

 but exhibited that remarkable compression of their distal portion 

 which characterizes the corresponding bone in the Batrachia : they 

 likewise have the longitudinal impression along the middle of the 

 flattened surface. The length of the more perfect shaft is 2 inches 

 1 line. The precise nature of the broad fiat bone, Mr. Owen had 

 not determined. 



"With respect to the osseous dermal scuta, Mr. Owen remarks, 

 that though they form a striking instance of the Crocodilian affinities 

 of the Leamington fossil, yet as these detached superficial bones are 

 the most liable to be separated from the fragmentary skeleton of the 

 individual they once clothed, the negative fact of their not having 

 been found associated with the remains of the Labyrinthodon in 

 other localities proves nothing in regard to a difference of dermal 

 structure between the Leamington and Warwick species. Indeed 

 no anatomist, he says, can contemplate the extensive development 

 and bold sculpturing of the dermal surface of cranial bones in the 

 Labyrinthodon pachygnathus and L. leptognathus without a suspi- 

 cion, that the same character may have been manifested in bony 

 plates of the skin in other parts of the body. Admitting for a 

 moment this structure to be proved, to what extent, asks Mr. 

 Owen, does it affect the. claims of the Labyrinthodon to be admitted 

 into the order of Batrachians, in which every known species is 

 covered with a soft, lubricous and naked integument, without scales 

 or scuta? ? In reply, he says, that the skin is the seat of variable 

 characters in all animals ; and, apart from the modifications of the 

 osseous and dental systems, and other intimate organs, is apt to 

 mislead the naturalist who is in quest of the real affinities of a 

 species : and he instances the Trionyx, as an example of a soft- 

 skinned animal among Chelonian reptiles. Lastly, Mr. Owen 

 shows, that, previously to the discovery of the fossils described in 

 this memoir, the only Batrachian remain which had been found in 

 beds anterior to the epoch of the Molasse is the fragment of a 

 skull, on which Prof. Jaeger founded his Salamandroides giganteus. 



March 10. — A paper " On the Geological Structure of the Northern 

 and Central Regions of Russia in Europe," by Roderick Impey Mur- 

 chison, Esq., P.G.S., and M. E. de Verneuil, V.P.G.S. of France, 

 was commenced. 



