31 



fonffirosti'ls, in the more rapid increase of the vertical breadth of the 

 jaw. Opposite the ninth tooth, e. p., the depth of the jaw equals two- 

 fifths of the length in advance of that tooth, whilst in the Pt. longi- 

 rostris it is only two-sevenths. The contour of the upper border of 

 the jaw in the Pt. Cuvieri differs from that in both the Pt. longi- 

 rostris, Pt. crassirostris, and Pt. Gemmingi, in sinking more sud- 

 denly opposite the ninth, eighth and seventh teeth, than it does along 

 the more advanced part of the jaw ; a character which, while it affords 

 a good specific distinction from any of those species, indicates the 

 hinder parts of the head that are wanting in the present specimen to 

 have been shorter and deeper than in the Pt. longirostris. 



The first pair of alveoli almost meet at the anterior extremity of 

 the jaw, and their outlet is directed obliquely forwards and down- 

 wards ; the obtuse end of the premaxillarj' above these alveoli is about 

 two lines across. The palate quickly expands to a width of three 

 lines between the second alveoli, then to a width of four lines between 

 the fourth alveoli, and more gradually, after the ninth alveoli, to a 

 width of six lines betweeu the eleventh alveoli : here the palate ap- 

 pears to have been slightly crushed ; but in the rest of its extent it 

 presents its natural form, being traversed longitudinally by a mode- 

 rate median ridge, on each side of which it is slightly concave trans- 

 versely. It is perforated by a few small irregular vascular foramina. 

 There are no orifices on the inner side of the alveoli ; the successional 

 teeth emerge, as in the Crocodiles, from the old sockets, and not, as 

 in certain Mammalia and Fishes, by foramina distinct from them. 

 The second and third alveoli are the largest ; the fourth, fifth and 

 sixth the smallest, yet they are more than half the size of the fore- 

 going, with which the rest are nearly equal. The outlets of the alveoli 

 are elliptical, and they form prominences at the side of the jaw, or 

 rather the jaw sinks gently in between the alveoli, and is continued 

 into the bony palate without any ridge, the vertical wall bending round 

 to form the horizontal plate. The greatest breadth of the under sur- 

 face of the jaw, taken from the outside of the alveoli, varies only from 

 seven lines across the third pair to nine lines across the eleventh pair 

 of alveoli ; and from the narrow base the sides of the jaw converge 

 with a slight convexity outwards at the anterior half of the fragment, 

 but are almost plane at the deeper posterior half, where they seem to 

 have met at one acute superior ridge ; indeed such a ridge is con- 

 tinued to within an inch of the fore part of the jaw, where the upper 

 border becomes more obtuse. 



The whole portion of the jaw appears to consist of one uninter- 

 rupted bone — the premaxillary ; the delicate crust of osseous sub- 

 stance, as thin as paper, is traversed by many irregular cracks and 

 fissures, but there is no recognizable suture marking off the limits of 

 a maxillary or nasal bone. The bone offers to the naked eye a fine 

 fibrous structure, so fine as to produce almost a silken aspect, the 

 fibres or striae being longitudinal, and impressed at intervals of from 

 two to six lines by small vascular foramina. 



Having premised so much with reference to the characters of the 



