246 ' BRIIISH FOSSIL REPTILES. 



that of the Pt. giganteus is 2 inches 3 Hncs ; the total length of the head of the 

 Pt. crassirostris is 4 inches 8 lines, that in the Pt. giganieus, restored on the same 

 scale, would be 9 inches, and the proportions on which this calculation is made are 

 much more likely to have been maintained, than those of the Pt. longirostris in 

 reference to the more gigantic Pt. Cuvieri ; but the teeth are absolutely shorter, and 

 relatively much smaller, than in the Pt. crassirostris. 



The lower jaw, fig. 5, has an obtuse rounded termination anteriorly like the upper 

 one, fig. 4, but is a little narrower there, and is flatter, its under part being less convex 

 than the corresponding exposed part of the upper jaw is above : the median inferior 

 ridge behind this part is more suddenly developed than that upon the upper jaw, and 

 the progressively deepening sides of the lower jaw are bent inwards before they form 

 the ridge, being convex near the alveoli, and becoming concave at the base of 

 the ridge, in the transverse direction : and this modification does not appear to 

 be the result of accidental pressure. The sohd or confluent symphysis has an 

 extent of more than 2 inches, but the bone is too much broken away at its back 

 part to determine its precise extent: it is evident, however, that the rami diverging 

 from it were of less vertical extent than the ridged part of the symphysis from which 

 they diverge, and this character is also shown in the lower jaw of the Pt. longirostris, 

 and Pt. Gemmingi. On the right side of the lower jaw, which is best preserved, there 

 are nine alveoli, and part of a tenth, corresponding in size and spacing with those 

 above. The inner alveolar wall extends so far inwards, horizontally, that if discovered 

 alone, it might well be mistaken for the palatal plate of an upper jaw. It is not 

 united with that of the opposite side to an extent corresponding with the bony palate 

 above ; but to what extent the symphysis of the jaw is continued backwards, the 

 specimen does not allow to be precisely determined. This broad inner alveolar plate 

 of the lower jaw is slightly concave transversely, forming a wide longitudinal channel 

 about two lines and a half in breadth along the inner side of the alveolar border : to 

 the extent to which it may be united to the opposite plate, a median longitudinal 

 ridge will be formed dividing the two channels ; and presenting a structure closely 

 corresponding with that of the palate above. 



The teeth are preserved, in situ, in some of the alveoli, of both the upper and 

 lower jaws. The enamelled crown is a less elongated and narrow cone than in either 

 the Pt. Cuoieri, or the Pt. crassirostris, and it is less compressed ; it does not exceed 

 one line and a half in length. The fang is longer, and after a slight expansion main- 

 tains the same diameter, or contracts a little towards its basal termination. The 

 smooth polished coronal enamel shows the same extremely fine raised striae, with an 

 irregular course and wide intervals, as in the teeth of Pt. Cuvieri. The basal 

 cement has a more irregular external surface. The fractured tooth in the sixth alveolus 

 of the left side shows well the form of the transverse section at the base of the crown, 

 and the proportional size of the pulp-cavity. This, as usual, is occupied by a sparkling 



