THE WASATCH FAUNA. 
281 
This I have called the ProtencepJiala* with the following definition:—Cere¬ 
bral hemispheres smooth, small, leaving not only the cerebellum, but the 
middle brain, exposed behind, and contracting into the very large olfactory 
lobes in front. Cerebellum very small and flat; middle brain large. This 
character is sustained by that of the ankle-joint, which, existing in two such 
distinct divisions as the Amhlypoda and Creodonta, may be found to character¬ 
ize the entire subclass, but this is not yet certain. It is as follows:—Tibio- 
astragalar articulation flat and without groove or segment of pulley. 
This subclass stands below the Lyencephala in its position, approximat¬ 
ing the Reptiles in the points above mentioned more nearly than the latter 
do. It includes two orders, one Ungulate, the Amhlypoda, the other Ungui- 
culate, the Bunotheria. To the former belong the suborders Pantodonta 
and JDinocerata; to the latter, the Creodonta, and probably the Tillodonta and 
Tceniodonta. Whether the Mesodonta belong to it is not certainly ascertained, 
while the Insectivora do not belong to it, as they are rightly placed in the 
subclass Lissencephala. 
The relation of these various characteristics to the question of descent 
is obvious, and it is believed that, through the study of this fauna, more 
intelligent phylogenies are possible than heretofore. In 1868, I wrote as 
followst on the “law of homologous groups”: “In the same manner, the 
development of the convolutions of the brain does not define groups of the 
highest rank, since it progresses chiefly during the later periods of embryonic 
life.Owen has endeavored to define the primary divisions of 
the Mammalia by the character of these convolutions, whereas they only 
define the subgroups of the orders; for we have lissencephalous (smooth¬ 
brained) Monkeys—certain Lemurs—and smooth-brained Ruminants [Artio- 
dactyla], i. e., the extinct Brachyodon and AnoplotJierium, according to Lar- 
tet and Gratiolet.If now, through some topographical change, 
the whole series of Mammalia between the smooth-brained and convolute¬ 
brained were lost to us, as by the elevation of land and the absence of 
favorable localities or bodies of water for the preservation of their remains, 
we would have to study two homologous groups with the heterologous 
*Proc. Amer. Philos. Soc., March, 1877. 
t Origin of Genera, pp. 62, 63, 79. 
