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, i.e., 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 Eobasileus 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 the 

 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 Palceotheriidce, 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 Nasua 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 Nasua 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. \ 



* On the Short-footed Ungulata of Wyoming, page 3. 

 t 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 palaeon- 

 tologists. 



