530 Mr. Owen on species of 



thinned off, apparently for supporting the corresponding margin of the nasal 

 bone : two or three wide, deep, subangular longitudinal grooves run nearly parallel 

 with this border, external to which other shorter and similar grooves radiate 

 towards the outer margin of the fragment. In no species of Crocodile is the 

 external surface of the cranial bones sculptured by such deep and wide incisions, 

 or excavations, relatively to the size of the bones. The ridges between these 

 grooves in the Lahyrinthodon have their edges rounded off. The depth of these 

 inflections of the external surface of the bone brought to mind the corresponding 

 inflections of the external surface of the teeth which form so striking a character- 

 istic of the present extinct Batrachian family. The interspace between the sculp- 

 tured maxillary bone and the co-extensive palatine plate here preserved, is nowhere 

 more than two lines and a half in depth ; but the two plates may have been un- 

 naturally approximated by pressure. The wide and shallow nasal cavity is occupied 

 by the matrix (PI. XLIII. fig. 10, e). 



The chief deviation from the Crocodilian type of structure which the present 

 fossil presents, is the continuation of the palatal plate (&) of the intermaxillary 

 bone for some distance, about an inch, to the outer side of the base of the external 

 plate or process. 



In the Crocodiles the external wall of the intermaxillary bone rises from the 

 outer border of the palatal process, and is united by the whole of its posterior 

 margin with the maxillary bone. A different structure of the intermaxillary 

 bone prevails in the Batrachia : here the external is not co-extensive with the 

 internal or palatal plate, but it rises from a longitudinal tract traversing the 

 middle of the palatal plate, in the form of a compressed process, leaving an 

 interspace between its outer margin and the maxillary bone : in the Frogs there is 

 likewise an interspace between the external plates of the two intermaxillary bones, 

 which does not exist in the Menopome, among the perennibranchiate Batrachia. 

 Now, in the Lahyrinthodon, the intermaxillary bone presents the same peculiar 

 modification of the Batrachian condition of this bone as in the higher organized 

 Batrachia. The palatal process of the intermaxillary, for example, is extended 

 beyond the outer plate, both externally (PI. XLIII. fig. 9, &), and, but in a less 

 degree, internally, where it forms part of the boundary of the anterior palatal 

 foramen (fig. 9, c), whence the outer plate rises in the form of a compressed pro- 

 cess from a longitudinal tract (fig. 9, a), on the upper part of the palatal process. 

 The outer plate in the specimen is broken off" near its origin, and the fractured sur- 

 face gives the breadth of its base, stamping the fossil with a Batrachian character 

 conspicuous above all the Saurian modifications by which the essential nature of 

 the Lahyrinthodon appears at first sight to be masked. 



Anterior frontal. (PL XLIII. fig. 11.) — With the indications of Crocodilian affi- 

 nities in the maxillary portion of the cranium just described, we cannot feel sur- 



