Labyrinthodon /rom Warwickshire, 517 



antero-posteriorly. The large anterior tooth (PI. XLIII. fig. 2, «) is three times 

 the size of the first of the serial teeth which succeeds it, and the size of the serial 

 teeth gradually diminishes as they are placed further back, so that the eighth tooth, 

 counting the sockets from the first, is little more than half a line in diameter at its 

 base ; beyond this the teeth are of equal size, slender in proportion to their length, 

 and gradually diminishing from the middle of the crown to the apex, which is not 

 very acute where entire ; a linear pulp cavity is continued along the centre of the 

 tooth, nearly to this part. The transverse section of the apical two-thirds of the 

 tooth is cyUndrical, its outer surface smooth ; the basal third is fluted, as in the 

 teeth of the lower jaw ; the outer wall of the socket is anchylosed to this fluted 

 base, and slightly excavated in the interspaces of the teeth that are in place. From 

 the flatness and thinness of the maxillary bones the sockets of the teeth are neces- 

 sarily shallow. The length of the common-sized serial teeth is about two lines, 

 their greatest diameter one-third of a line ; the diameter of the base of the large 

 internal anterior tusk is two lines and a half. 



The outer surface of the maxillary bone begins to bend from the perpendicular 

 almost immediately above the alveolar process, and is continued through the rest 

 of its extent in a nearly horizontal plane. The whole breadth of the left upper jaw 

 appears to be included in the fossil for the antero-posterior extent of an inch oppo- 

 site the middle of the dental series. The breadth of this part from the median 

 longitudinal suture to the external alveolar process is one inch three lines ; two 

 inches and a half is therefore the breadth of the skull at this part. The upper jaw 

 gradually expands to the posterior part of the fragment, where it is one inch and a 

 half in breadth on the left side ; the anterior part of the fragment, which contains 

 the large tusks, slightly expands or inclines outwards. Where the upper jaw is 

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

 maxillary bone by a longitudinal harmonia running nearly parallel with the median 

 one ; the bone so defined corresponds with the position of the nasal bone in the 

 Crocodile. The whole of the outer surface of the bones here described is sculptured 

 with large irregular grooves and sinuses. One of the largest grooves, which is an 

 angular and not a rounded furrow, runs nearly parallel with the alveolar process, 

 between two and three lines above it, defining it, as it were, from the upper and 

 flat surface of the jaw ; a second principal furrow, as wide but less angular than 

 the outer one, commencing at the posterior part of the fragment, a line and a half 

 distant from the outer one, inclines inwards as it advances forwards with a slightly 

 irregular course, and terminates in the fragment preserved at the naso-maxillary 

 suture. The above two principal grooves are separated by a longitudinal row of 

 elliptical pits, which increase in size as the grooves diverge, and the wider anterior 

 interspace is occupied by additional smaller pits. The portion of the upper maxil- 

 lary bone included between the oblique groove and the nasal suture is marked with 



VOL. VI. SECOND SERIES. 3 X 



