6 
On the Phylogeny of the Mammalian Orders. So much light is thrown 
on this subject by the researches into the structure of the fossil mam- 
malia of the Eocene formation, that it seems opportune to call attention 
to.the subject. I deem it demonstrated to a certainty, that the case with 
the mammals of this formation is the same as with the reptiles of the 
Trias, z.¢., that the family types are all more generalized, and the orders 
not nearly so widely distinguished as in later periods of the world’s 
history, 
The succession of forms which has terminated in the horse, has been 
clearly pointed out by Prof. Huxley, as well as the line which has given 
the world the beautiful order of the Artiodactyla ; but the approximate 
lineal predecessors of the Proboscidia, of the Ungulate animals as a whole, 
of the Quadrumana (including man), and of the Carnivora, have not 
been clearly pointed out. 
The genus Hobasileus has been shown* to be a Proboscidian which 
combines some important features of the Perissodactyla with those of its 
own order, thus standing in antecedent relation to the elephants, etc., of 
the present day. The number of such characters was shown to be some- 
what increased in Bathmodon, which therefore stands still nearer to tke 
common point of departure of the two orders. This point is to be found 
in types nearer the clawed orders (Unguiculata), in the number of their 
digits (4-5), and in which the transverse and longitudinal crests of the 
molar teeth are broken up into tubercles more or less connected, either 
type of dentition being derived according as such tubercles are expanded 
transversely or longitudinally. We have several genera which answer 
this description so far as the teeth are concerned, but unfortunately the 
digits are unknown ; such are Oligotomus, Orotherium, etc. 
The type of Tomitherium already described, evidently stands between 
Lemurine monkeys and such small allies of Paleothertide, with conic- 
tubercular teeth, and which abound in the Eocenes of Wyoming and 
France. The dentition of the two types is indeed but little different in 
the Quadrumanous and Ungulate types respectively, being a continuous 
series of I. 2 or 3; C. 1, P.M. 3-4; M. 3; the canines but moderately 
developed. 
A comparison with Naswa reveals no distant affinity. As above re- 
marked, the fore-limb presented a great similarity in this genus and 
Tomitherium. The teeth, though less numerous, in the molar series have 
the cutting type anterior and tubercular posterior, in both genera. 
Notharctus, Leidy, resembles Nasuwa still more than does Tomitherium, 
and occurs in the same Eocene strata. Prof. Leidy originally regarded it 
as a Carnivore, and subsequently (Hayden’s Survey Montana, 1871) 
placed it among Ungulates. He was probably nearly correct on both 
occasions, and that only a technical line will ultimately decide whether it 
be not a monkey.t 
* On the Short-footed Ungulata of Wyoming, page 3. 
+ Dr. Lockwood, of Rutger’s College, in a recent number of the Popular Science Monthly, 
expressed serious suspicions of the Quadrumanous relationships of the Coati, little thinking at 
the time that the specimens to confirm his view were at that moment in the hands of paleon- 
' tologists. 
