ON BRITISH FOSSIL REPTILES. 183 



described in my Memoir read before the Geological Society, and in which 

 additional, and, as it seems to me, conclusive proof is given of the Batrachian 

 nature of the genus to which those fossils belong ; with the establishment of 

 five distinct species, one of which is most probably identical with the Masto- 

 donsaurus salamandroides of Prof. Jaeger. 



It is scarcely necessary to repeat the reasons which I have given to show 

 that the generic denomination Mastodonsaurus cannot be retained ; first, it 

 unavoidably recalls the idea of the mammalian genus Mastodon, or else a 

 mammilloid form of tooth, whereas, all the teeth of the reptile so called are 

 originally, and most of them are permanently of a cuspidate and not of a 

 mammilloid form ; secondly, because the second element of the word, saurus, 

 indicates the genus to belong to the Saurian and not to the Batrachian order 

 of reptiles. For these reasons I have proposed to designate the genus in 

 question Labyrinthodon, in allusion to the peculiar and characteristic struc- 

 ture of the teeth. 



The specimens which I have examined are referable to five species, viz. 

 \. Lahyrinthodon salamandroides; 2. L. leptognathus ; 3. L. pachygnathus ; 

 4. L. ventricosus ; and 5. L. scutulatus : and I shall here briefly notice the 

 characters exhibited by the bones assignable to the 2nd, 3rd, and 5th species. 



Lahyrinthodon leptognathus. — The remains which I consider as portions of 

 this species, consist of fragments of the upper and lower jaws, two vertebrae, 

 and a sternum. They were found in tlie sandstone quarries at Coton End, 

 near Warwick. 



The portions of the upper jaw show that the maxillary or facial division of 

 the skull was broad, much depressed, and flattened, resembling the skull of 

 the gigantic Salamander and of the Alligator ; and the outer surface of the 

 bones was strongly sculptured, as in the Crocodilian family, but of a relatively 

 larger and coarser pattern. One portion of the upper jaw contains the an- 

 terior moiety of the single row of small teeth, or thirty sockets, and the base 

 of one of the great anterior tusks. The bases of the serial teeth project 

 directly from the outer wall of the shallow socket, there being no alveolar 

 ridge external to it. The large anterior fang is three times the size of the 

 first of the serial teeth, and the size of these gradually diminishes as they are 

 placed further back ; the length of the common-sized teeth being about two 

 lines, and the greatest breadth one-third of a line. The apical two-thirds of 

 each tooth is smooth, but the basal third is fluted, and anchylosed to the outer 

 wall of the socket. The breadtli of the upper jaw, opposite the middle of the 

 dental series, was two inches six lines ; in proceeding backwards the jaw gra- 

 dually expands to three inches, and in proceeding forwards narrows, but in a 

 less degree towards the anterior extremity, and then slightly widens or in- 

 clines outwards on account of the large tusks. Where the upper jaw is entire, 

 ^ portion next the median suture, four lines in breadth, is separated from the 

 maxillary bone by a longitudinal harmonia, and corresponds with the position 

 of the nasal bone in the Crocodile. 



On comparing the structure of the cranium of the Lahyrinthodon with the 

 existing Batrachiaus, it is true that an important modification will be found 

 to exist. In botli the caducibranchiate and perennibranchiate species, tiie 

 upper maxillary bones do not extend horizontally over the upper surface of 

 the skull, but leave a very wide interval between the maxillary and nasal 

 bones ; and the palatal processes of the former contribute as little to form the 

 floor of the nasal cavity : in the Crocodiles, on the contrary, the palatal pro- 

 cesses of the maxillary bones extend horizontally inwards, and meet at the 

 middle line of tlie roof, forming an unbroken floor to the nasal cavity. In 

 tiie Lahyrinthodon the superior maxillary bones, as already shown, extend in- 

 wards to the nasal bone, constituting with it a continuous roof to the nasal 



