GEOLOGICAL SUEVEY OF THE TERRITORIES. 645 



but whicli are somewhat mixed in cliaracter. Thirteen represent genera 

 {Baena, Anostira, Plastomenus, Axestus) which are extinct and general- 

 ized in character, the first three in an especial manner, as has been 

 pointed out. 



The orders of the fishes are equally well distinguished, and so far as 

 known, the types differ only in minor respects from those at present in- 

 habiting iSTorth American waters. Generalized types are unknown, ex- 

 cepting, perhaps, in the yery highest division, {^rismatopterus, Asine- 

 ops.) 



As a result of this and other palseontological investigations conducted 

 largely in North America, and substantiated by those in other countries, 

 the i)eriods of establishment of the existing order of things in the his- 

 tory of the vertebrata, may be stated as follows : 



The recent orders of fishes were in existence in the Cretaceous period, 

 and probably earlier. Their period of evolution was in the Devonian, 

 and perhaps in the Carboniferous periods. The existing orders of rep- 

 tiles were all established in the Eocene; the period of evolution was 

 the three Mesozoic ages, especially the Trias. The orders of birds were 

 inchoate in the Cretaceous, but when they were fully diflerentiated is 

 unknown. The existing orders of Mammalia were established in the 

 Miocene period ; during the Eocene they were in process of diflereutia- 

 tion and were less or scarcely distinctly defined. 



On the PJiylogeny 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 later forms which has terminated in the horse, has 

 been clearly pointed out by Professor Huxley, as well as the line which 

 has given the world the beautiful ov diG:T of thQ Artiodacty la ; but the 

 approximate lineal predecessors of tbe Prohoscidia, of the Ungulate 

 animals as a whole, of the Quadrumana, (including man,) and of the 

 Carnivora, have not been deafly pointed out. 



The genus Uohasileus has been shown* to be a Proboscidian which 

 combines some important features of the Perissodaetyla with those of its 

 own order, thus standing in antecedent relation to the elephants', &c., 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 jjoint 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 ex- 

 panded transversely or longitudinally. We have several genera which 

 answer this description so far as the teeth are concerned, but unfor- 

 tunately the digits are unknown; such are Oligotomus, Orotherium, &c. 



■The type of Tomitherium, already described, evidently stands between 

 Lemurine monkeys and such small allies of Palwotheriidce, with conic- 

 tubercular teeth, and which abound in the Eocenes of Wyoming and 

 France. The dentition of the two types is indeed but little diiferent in 

 the Quadrumanous and Ungulate types respectively, being a continu- 



" On tlie short-footed Uagulata of Wyoming, page 3. 



