204 CONDYLARTHRA—PROTOGONIA CHAP. 
Creodonta. It has, as in Phenacodus, no orbital ring. The 
humerus resembles that of a Carnivore rather than that of an 
Ungulate. The carpus and tarsus are serial. The fibula articu- 
lates with both the calcaneum and the astragalus, which is not 
the case with Phenacodus. It is suggested that these animals 
are ancestral forms of the Chalicotheres. In the brain the 
hemispheres do not cover the cerebellum. 
More primitive apparently than Phenacodus was the less-known 
genus Luprotogonia, or Protogonia ' as it has been called. The best- 
known species is HL. puercensis, so called from its occurrence in the 
Puerco beds of the American Eocene. It was a slender, long- 
limbed creature, smaller than Phenacodus, with a long and heavy 
tail as in that animal. Like Phenacodus it was semiplantigrade, 
and shows more likenesses to the Creodonta. The skull is only 
known by a part of the lower jaw with teeth, and by the teeth of the 
upper jaw. The vertebrae are not entirely preserved, but enough 
remain to show that the animal had a tail of 16 or 17 inches, which is 
a considerable length when compared to its height, about a foot at 
the rump. In the fore-limb the most noteworthy point is that the 
ulna has a convex posterior border as in the Creodonts, the same 
border in Phenacodus being concave. ‘The humerus is slender, with 
less-marked tuberosities. The fifth digit seems to have been less 
reduced. The phalanges seem to have borne horny sheaths some- 
what intermediate between hoofs and claws. The pelvis is 
described as being, as 1s also that of Phenacodus, rather like that of 
the Creodonta. The right hind-limb is known in all its details. 
It appears that the bones are not serial but interlocking; this, 
however, on the views with regard to the relations of these two 
forms of tarsus mentioned on p. 198, does not militate against 
regarding Huprotogonia as the ancestor of the genus Phenacodus. 
The third toe is the pre-eminent one, the animal thus being 
Perissodactyle. The lateral digits are larger than in Phenacodus, 
and the metatarsals and the phalanges are slightly curved, which 
is again a Creodont character as compared to the perfectly straight 
corresponding bones of Phenacodus. It seems evident that this 
animal is to be looked upon as a more ancient type than Phena- 
codus, even if not as its actual ancestor. 
Another group of the Condylarthra contains the genus 
Pertipychus and some others. Periptychus has the full dentition 
1 See W. D. Matthew, Bull. Amer. Mus. Nat. Hist. ix. 1897, p. 303. 
