31 
longirostris, in the more rapid increase of the vertical breadth of the 
jaw. Opposite the ninth tooth, e. g., the depth of the jaw equals two- 
fifths of the length in advance of that tooth, whilst in the P¢. longz- 
rostris it is only two-sevenths. The contour of the upper border of 
the jaw in the P¢. 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 P#. 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 premaxillary 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 between 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 strize 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 
