Skull of Tritylodon longeevus, Owen. 287 
On the underside of the skull (text-fig. 3) the sutures 
separating the premaxillaries from the maxillaries and the 
palatine processes of the latter are almost certain (comp. 
Owen, 1884, p. 147) ; but the suture between the palatines 
and the maxillaries is very doubtful. 
Thave still to add that 1 can confirm the statement of Broom 
(comp. Broom, 1910, p. 762) that there are in Tritylodon not 
two but three incisors. Indeed, in the front of the two 
broken great incisors and near to the point where the two 
premaxillaries are meeting one another there are two small 
teeth-sockets (text-fig. 3). But Broom’s statement (7b. 
p. 762) that there are seven and not six molars in T'ritylodon 
I cannot accept, because the limit of the last molar on the 
right side isa sharp one, and no plain trace of a molar behind 
itis to be seen. I suppose, in consequence, the dental formula 
ot Tritylodon to be 2 3, pm 1, m 5 *. 
According to my preceding statements, and to the previous 
statements of Owen, Seeley, Osborn, and Broom, I add here, 
in conclusion, a review of the mammalian and reptilian 
characters of Zritylodon. 
I. Mammalian Characters. 
1. Divided roots of molar teeth ; 
2. Multituberculate teeth ; 
3. Straight and parallel rows of teeth ; 
4, No postfrontal bone. 
From these four characters, the first is still the best proof 
for the mammalian character of T'’ritylodon, no theromorphous 
reptile being known with divided teeth-roots. But, as some 
doubts have been expressed about this division f, the prepara- 
tion of the molar toothin Tritylodon by Owen has been some- 
what enlarged, and the new preparation shows (comp. the 
photograph in Pl. X. fig. 2) that no doubt about that division 
can be entertained, the bone between the two roots un- 
doubtedly not being dentine (it has the same colour as the bone 
in front of the forward root). As a new corroborative proof 
wrong. The posterior part of the skull would be in both cases almost 
the same (comp. the restoration of it in text-fig. 1 with the restoration 
of Broom in Broom, 1914, fig. 1, p. 119). ; 
* In 1914 Broom gives the dental formula of Titylodon as being 
probably 7 3, ¢ 0, p 4, m 3 (comp. Broom, 1914, p. 120). 
+ Comp. H. Gadow, ‘Amphibia and Reptiles,’ London, 1901, p. 309. 
