196 PROF. OWEN ON A THERIODONT REPTILE 
sandstone, which Hugh Falconer made known to us under the name 
of Leptorhynchus crassidens *. 
Amongst the more fragmentary evidences of this species was a 
portion of the lower jaw corresponding with the subject of fig. 6, 
Pl. XI., and lodging a canine tooth of equal size. I therefore caused 
a similar section to be made of this tooth and its socket. The canine 
in place had its summit worn to a certain obtuseness; it had eyi- 
dently been some time in use; but no long or tapering root de- 
scended from the crown. ‘The implanted base was widely open, and 
within the similar wide and conical pulp-cavity had passed the crown 
of the next toothin succession. Of this crown the apical cap or shell 
was calcified, the base widely open, and the pulp, replaced by disco- 
loured matrix, had occupied the cavity of the growing tooth. On the 
inner side of the base of this cavity a reserve socket had begun to be 
formed around the matrix of a third tooth, or second in succession to 
the one inuse. The track of the germ, originally budded off from the 
base of the old matrix, was reduced to a linear canal extending from 
the base of the socket into which the successional tooth had pushed 
its way, to that which was due to the absorption through pressure of 
the growing matrix of the tooth destined in its turn to force its way 
into the hollow, beneath the young tooth. 
The contrast between the Theriodont and the Crocodilian reptile 
in this important dental character was strikingly manifested in the 
sections of the large homologous tooth. 
I proceeded next to test the same character in the incisor and molar 
teeth. Figure 4, as before stated, represents the section of the root 
of the anterior upper incisor of 7itanosuchus ferow. Here, as in the 
canine, the root at first gradually diminished, and then more quickly 
contracted to a rather blunt point, 7. The pulp-cayity, p, became 
closed at a greater relative distance from this point than in the canine. 
Similar longitudinal or vertical sections were made of molar teeth 
from both ends of their series with similar results, as is exemplified 
in fig. 5 of an eleventh molar of the upper jaw, and by fig. 9 of a 
third lower molar. In the latter tooth the pulp-cavity, p, extends 
nearer to the closed end of the root than in the other sections. 
The evidence of successional teeth in the case of the upper incisors 
has already been given; but they are developed in distinct sockets, 
and do not penetrate wide unclosed pulp-cavities of the teeth in 
place and use, as in the Crocodilia. 
s Whether the more mammalian character of succession operates in 
the canine and molar teeth, as in the incisor series, no evidence has 
been extracted from the present Titanosuchian fossils. 
The ordinal character of the Crocodilian tooth, as above exempli- 
fied in recent and extinct species, I long ago defined, as consisting 
in the slight enlargement, or maintenance of the same breadth, of 
the root to its base, which is deeply excavated by a conical pulp- 
cavity extending into the crown, and is commonly either perforated 
or notched at its concave or inner side*. 
* Paleontological Memoirs, 8vo, i. 1868, p. 279. 
+ ‘Odontography,’ yol, i. p. 29], pl. 75. figs. 1, 2, 4a, 5, 
