This order includes certain large extinct Mammals from the later Tertiary deposits of South

Fig. 414.   Tillodontia. Side view of the skull of Tillotherium fodieus, with the lower jaw displaced downwards, one fourth of the natural size. (After Marsh.)

Fig. 414. - Tillodontia. Side-view of the skull of Tillotherium fodieus, with the lower jaw displaced downwards, one-fourth of the natural size. (After Marsh.)

Fig. 415   A, Right upper jaw of Toxodon Burmeisteri, and (B) left lower jaw of the same ; c Lower canine. (After Burmeister.) Greatly reduced in size.

Fig. 415 - A, Right upper jaw of Toxodon Burmeisteri, and (B) left lower jaw of the same ; c Lower canine. (After Burmeister.) Greatly reduced in size.

America, the true systematic position of which is still very doubtful; since they present affinities to the Ungulata, the Rodents, and the Edentates. The skull is massive and the dentition is very peculiar. The molars and praemolars are bent so as to be strongly convex outwards and concave inwards, with flat grinding-surfaces (fig. 415), and presenting the peculiarity that they are rootless and grow from persistent pulps. Canines are present in the lower jaw, but are of very small size (fig. 415, c) and are placed in the interval between the incisors and praemolars. In the upper jaw only the sockets for the canines are left. There are four upper and six lower incisors, which are separated by a wide diastema from the praemolars. The dental formula is:

i

2 - 2

; c

0 - 0

; pm

4 - 4

; m

3 - 3

=

38.

3-3

1 - 1

3 - 3

3 - 3

There is no third trochanter to the femur, but the structure of the manus and pes is quite unknown.

The only known genera are Toxodon and Nesodon.