192 PROF. OWEN ON A THERIODONT REPTILE 
The third tooth (ib. 73) was, in section, more nearly elliptical, 
with the long axis transverse to the jaw, 20 millims. by 12 millims. 
in the two diameters. An interval of 10 millims. separated 1t from 
the second tooth, 7 2. 
The fourth tooth (ib. 7 4), less regularly elliptical in section,’ was 
23 millims. by 17 millims. in the two diameters, which held the same 
relation to the alveolar border as the preceding teeth. The pulp- 
cavity, p, of the fourth tooth was 14 millims. by 10 millims. The 
interval between this and the third tooth was 18 millims. 
The fifth tooth (ib. c) showed a great increase of size, the two 
diameters being 2 inches by 14 inch, or 50 millims. by 35 millims. ; 
its section presented a less regular oblong shape, and the long 
diameter was inclined toward the longitudinal course of the alveolar 
border. ‘The long diameter of the pulp-cayity, p, is 34 millims. ; 
the transverse or short one is 20 millims. 
The thickness of the dentinal wall was pretty uniformly 10 millims. 
The indications of the osseous walls of the sockets of these teeth 
are marked 0, 0, in fig. 6. 
Comparing the evidence of the anterior teeth of the fossil mandible 
with the teeth in the corresponding part of that of existing reptiles, 
I found the nearest correspondence in Crocodilus vulgaris, Cuv. 
The mandibular symphysis varies in shape and relative length in 
existing Crocodilia, its shortness distinguishing the genera Cvo- 
codilus and Alligator from the genus Gavialis. But it offers cha- 
racters in regard to shape and proportions in different species of the 
broad-faced section of the order, where it is of least extent. It is 
shorter, for example, in proportion to its depth or vertical diameter, 
in Crocodilus vulgaris, Cuy., than in Crocodilus bombifrons and 
Crocodilus palustris ; and in its symphysial character I found that 
the present fragment of 7itanosuchus most resembled a specimen of 
Crocodilus vulgaris from a river opening upon the west coast of 
Africa. 
In Crocodilia the inner surface of the dentary element is impressed 
by a longitudinal groove which terminates forwards by indenting 
the symphysial surface. A similar groove indents the correspondiug 
surface of the dentary bone of Tvtanosuchus. It is, however, 
situated nearer the lower margin of the bone, less deeply indents 
the symphysial surface, and the lower border of the groove is less 
produced than in the recent Crocodiles compared. 
The seemingly lower position of the groove which, from its being 
covered, in Crocodiles, by the splenial element, I have called 
‘“‘splenial,” is due, in 7%tanosuchus, to the downward inclination of 
the inner alveolar wall of the incisive series of teeth. In the Croco- 
dilian mandibles compared this wall extends horizontally inwards 
for some way before bending down to the inner grooved surface, 
rendering such inner surface of minor relative extent than in Titano- 
suchus. The part marked h, fig. 6, sloping downwards to the groove, 
answers to a nearly horizontal flattened upper surface in Crocodilus 
vulgaris. 
In most existing broad-faced Crocodiles three teeth, reckoned as 
