This order has been established by Prof. Marsh for the reception of some singular Mammals from the Eocene Tertiary of the United States. The following are the characters of the order, so far as published: The molar teeth have grinding crowns; as in Ungulates, and may have distinct roots, or may grow from permanent pulps ; small canities are present in both jaws ; and each jaw carries two long scalpriform incisors, resembling those of Rodents in form and in growing from persistent pulps. The feet are plantigrade and pentadactyle, and the digits were apparently unguiculate. The femur has a third trochanter, and the radius and ulna and tibia and fibula are distinct bones.

The order includes two distinct families, - one, the Tillothe-ridae, having molar teeth with distinct roots; whilst the other, Stylinodontidae, possessed rootless molars, which grew from persistent pulps. All the known forms of the order are from the Eocene Tertiary, and the typical species seem to have been from one-half to two-thirds of the size of the Tapir.

The type-genus of the order is Tillotherium, which presents a remarkable combination of the characters of the Ungulata, Rodentia, and Carnivora. The general form of the skeleton most closely resembles that of the Carnivores, the skull being like that of the Bears in many respects, whilst the feet are five-toed, with the whole sole applied to the ground, and having ungual phalanges similar to those of the Ursidae. The brain-cavity is of small size, and the cerebral hemispheres did not extend over the cerebellum or the olfactory lobes. The orbits are not complete, but open into the temporal fossae. The praemolars and molars have grinding crowns, the canines are of small size, and the praemaxillae carried a pair of large scalpri-form incisors (fig. 414), which resemble those of the Rodents in having chisel-shaped crowns, and in growing throughout the life of the animal. As in Rodents, there is a corresponding pair of scalpriform incisors in the lower jaw. The dental formula is:

i

1 - 1

; c

1 - 1

; pm

3 - 3

; m

3 - 3

=

30.

1 - 1

1 - 1

2 - 2

3 - 3