872 GEOGRAPHICAL AND GEOLOGICAL DISTRIBUTION. 



ridge, one of which, at least, lies as much in the direct line of descent 

 of the tapir as it does of the horse. It will thus be seen that from 

 the evolutionary standpoint, or from the point which views rela- 

 tionship by descent as of equal importance with that which unites 

 forms solely through a community of general characters, family 

 lines could be traced among these earlier ungulates at points other 

 than where they have actually been drawn, and with fully as much 

 reason. For it can scarcely be gainsaid that the direct ancestors 

 of the horse, for example, would form as natural a group among 

 themselves as they now form three or four groups in the way they 

 have been scattered about. 



Other tapiroid forms, more or less closely related to the lophio- 

 dons, are Limnohyus and Palaeosyops, both from the Eocene ; 

 Chalicotherium, whose remains have been found in Oregon, and in 

 Eurasia from France to China, appears in the Oligocene and Mio- 

 cene. Approximately contemporaneous with the last, and embrac- 

 ing animals of the dimensions of the elephant, or even larger, 

 with certain resemblances to the rhinoceros, were the Menodon- 

 tidee, whose remains have been found in both hemispheres. Sev- 

 eral genera of this family Menodus, Titanotherium, Symborodon, 

 Brontotherium have been described, but it would appear that not 

 all of these are entitled to generic recognition. 



A group of highly specialised and abnormal forms of Perisso- 

 dactyla, concerning which there has been much diversity of opinion 

 expressed, and whose position in the zoological scale has not yet 

 been definitely established, is that of the Macrauchenidae, with the 



Hipparion, Anchitherium, Palseotherium. Dr. Max Schlosser, in an elaborate 

 review of the phylogenetic relationships of the Ungulata (" Morphologiscb.es 

 Jahrbuch," 1886), considers the equine line of descent to pass through Phena- 

 codus (as earliest form), Hyracotherium, Anehitherium, Mcrychippus, Hippa- 

 rion, and Pliohippus. Hyracotherium and Hipparion, and possibly also An- 

 chitherium, are assumed to be by origination American forms, which subse- 

 quently wandered over to Europe, but the relative appearance of these forms 

 on the two continents scarcely warrants this supposition. The same author- 

 ity identifies the American Mesohippus and Miohippus with Anchitherium, 

 and Protohippus with Hipparion ; Eohippus is considered to be probably 

 identical with Hyracotherium. By Mr. Wortman, on the other hand, who 

 first recognised in Phenacodus the earliest ancestor of the horse, and who 

 unequivocally identifies Orohippus with Hyracotherium, both Mesohippus and 

 Protohippus are considered to represent types of distinct generic value (" Kevue 

 Scientifique," June, 1883), 



