Labyrinthodon /rom Warwickshire. 529 



centre and the circumference of the tooth, where each terminates in a slight dilata- 

 tion. In like manner, the inflected folds, converging from the circumference of the 

 section, proceed inwards in a straight line to within one-fourth of the distance to 

 the central pulp-cavity. The inflected substance consists of the thinnest layer of 

 cement. The calcigerous tubes radiate according to the usual laws, and resemble 

 in diameter, in the width of their interspaces, in their secondary undulations, 

 their dichotomous bifurcations and small lateral branches, the same tubes in the 

 large tusk with the more complex labyrinthine structure. 



The external wall of this portion of the jaw is straight, and nearly flat ; and slopes 

 upwards and slightly inwards from the narrow ridge which runs along the outside 

 of the alveoli. The inner or palatal process of the jaw is as narrow as that of the 

 Labyrinthodon leptognathus, and terminates internally by a smooth, regularly 

 rounded, convex margin, which describes a slight concavity in the antero-posterior 

 direction, and most probably formed the external boundary of the posterior palatal 

 opening : the breadth of the palatal plate of the maxillary bone at the middle of 

 this fragment is four lines, but at each extremity of the fragment it is six lines. 

 At the posterior part of the fragment the palatal surface is flat, and impressed 

 with a few small pits : anteriorly it is traversed by a shallow longitudinal groove. 



This condition of the palatal process of the maxillary corresponds more closely 

 with that in the Frog than in any other existing reptile. In all the Batrachia the 

 palatal process of the maxillary bone is very narrow, and is not extended inwards 

 at any part to join the palatine bone, so as to complete the bony roof of the mouth ; 

 but the inner boundary of the palatal process in the Frog is more parallel with the 

 alveolar ridge ; and a portion, corresponding in extent with the present fragment, 

 would not give that concavity of the inner border of the palatal process which the 

 present fragment presents 



I suppose, therefore, that the palatal process here must have extended inwards 

 at the anterior part of the maxillary, and probably so as to join the palatal bone, 

 as in the Lab. leptognathus, and agreeably with the traces of an extended bony 

 floor of the nasal cavities exhibited in the portion of the upper jaw which comes 

 next to be considered. 



This characteristic fossil, which is from the quarry at Coton End, includes a 

 considerable portion of the left maxillary and intermaxillary bone, and shows the 

 lateral contour of the anterior palatal foramen (PJ. XLIII. figg. 9 and 10). The 

 superior or external plate of the intermaxillary bone is broken away, but the ex- 

 ternal plate of the maxillary bone remains, together with the internal or palatal 

 plate, in the portion of that bone which is here preserved. The outer margin of 

 the present fossil is impressed with a portion of a wide groove, having the same 

 sinuous contour as the long oblique groove in the fragment of the upper jaw of the 

 smaller species of Labyrinthodon. The inner border of the fragment is obliquely 



