1881.] Geology and Paleontology. 1017 
(From the American Naturalist, December, 1881.) 
GHOLOGY AND PALZONTOLOGY. 
A NEW TYPE OF PerIssopactyLa.—lIn a paper on the “ homol- 
ogies and origin of the molar teeth of the Mammalia Educabilia, 
published in March, 1874,1 I ventured the generalization that 
the primitive types of the Ungulata would be discovered to be 
characterized by the possession of five-toed plantigrade feet, 
and tubercular teeth. No Perissodactyle or Artiodactyle mam- 
mal was known at that time to possess such feet, nor was 
any Perissodactyle known to possess tubercular teeth. Shortly 
after advancing the above hypothesis, I discovered the foot struc- 
ture of Coryphodon, which is five-toed and plantigrade, but the 
teeth are not of the tubercular type. For this and allied genera, 
I defined a new order, the Amdlypoda, and I have published the. 
confident anticipation that genera would be discovered which 
should possess tubercular (bunodont) teeth. This prediction has 
not yet been realized. I now, however, record a discovery, which 
goes far towards satisfying the generalization first mentioned, 
and indicates that the realization of the prophecy respecting the 
Amblypoda, is only a question of time. 
In 1873, I described from teeth alone, a genus under the name 
of Phenacodus, and although a good many specimens of the 
dentition have come into my possession since that date, I 
have never been able to assign the genus its true position in the 
mammalian class. The teeth resemble those of suilline Ungu- 
lates, but I have never had sufficient evidence to permit its refer- 
ence to that group. Allied genera recently discovered by me, 
have been stated to have a hog-like dentition, but that their posi- 
tion could not be determined until the structure of the feet shall 
- have been ascertained. 
In his recent explorations in the Wasatch Eocene of Wyoming, 
Mr. J. L. Wortman was fortunate enough to discover a nearly 
entire skeleton of a Phenacodus very near the typical P. primevus, 
which presents all the characters essential to a full determination 
of its place in the system. The unexpected result is, that this 
genus must be referred to the order Pertssodactyla, and that, with 
its allies, it must form a special division of that order correspond- 
ing in the tubercular characters of its teeth with the bunodont or 
suilline division of the Artiodactyla. In this character, however, 
there is a closer gradation than in the case of the Artiodactyla, 
1 Journal of the Academy of Natural Sciences Philadelphia. 
2 Paleontological Bulletin No. 17, Oct., 1873, p. 3; also, Report G. M. Wheeler, 
U.S. Engineers Expl. W. 100 Mer., iv, p. 174—1877. 
VOL, XV.—NO., XII, zo 
