Tin; MAMMALIA OF THE UINTA KOKMATION. 5il 



unique, in the fact that wliile the scaphoid has acquired an extensive magnum facet, 

 the hinar is extremely small ; the magnum is large and not only excludes the huiar 

 fi-oin the uncifoi-m, but actually has a cuneiform facet. Burmeister describes facets 

 for latei'al digits upon the pes.* The metapodials are strongly keeled. 



Schlossert lays great sti'ess upon the jJrimitive character of this animal as shown 

 in the serial disposition of the foot bones and the epicondylar foramen of the humerus. 

 In his earlier paper (Zool. Anz., p. 083), he placed this genus with the Perissodactyla; 

 later he separated it: "Fasst man alle diese Merkmale zusamraen, so kann man kauin 

 entschliessen Macrauchenia den Perissodactylen bcizuziihlen " (Morph. Jahrb., Bd. 

 XII, 188(3. p. 22). Upon this it may be observed that the arrangement of the carpals 

 is not serial, as he intimates, but has a peculiar adaptive displacement. The fibulo- 

 calcaneal facet may be considered a secondary character (sec p. 533). We can in 

 fact only conjecture the phylogenetic position of this genus, with its extraordinary 

 mixture of characters. Upon the whole it is more nearly related to the perissodactyl 

 than to any other phylum, and is possibly an offshoot of the primitive mesaxonic 

 stem, separating from the main line at a period corresponding to the Wasatch. 



111. THE PERISSODACTYLA. 



When we examine the Diplarthra as a whole, after reviewing the unrelated and 

 widely divergent groups which have already been considered, in which the displace- 

 ment of the carpals and tarsals presents little or no analogy, we find in contrast a 

 very striking unifbi'mity in the displacement of the upper elements to the outer side, 

 *'. e., in the carpus, the scaphoid a i' t i c u 1 a t e s with the magnum in the 

 same degree that the lunar a r t i c ula tes wi t h the unciform; in the 

 tarsus, the astragalus invariably extends upon the cuboid. This 

 is the universal law of displacement which is subject to variation in degree only. It 

 characterizes the stem forms of every family, ami is secondarily modilied by growth 

 arising from special causes. 



We may begin with a tyi)e in which the displacement is least extreme, and will 

 here consider only the Perissodactyla. 



* Op. pi/., p. 205, "01>i;leii-li iliirrnurhenia nur dn-i rnllstandigt- Zi-hi-n .-im jnleni Kussc lic^il/.l, so siiul iloili Urstcn 

 von zwci ftniliTen, wenigHK^ns am Ilintcrfu^so vorlmmlen gfwiscn. wic ilic Cii-lcnk rucollcii iiin A^'lragiilns innl Nnvini- 

 larc, glcich wic am Cul>oi(lfiim iKiweiscn." 



t Ziir Stivmm<>u'>-<l)ifhli- iI>t Iliillliicri'. Zool. Anzcijr.r, X.>. 210, 1885, |i. 68:1. Al»<), Bi.ilnigc /.in K<nnini« 

 ilrr Stiimmcsgcschiclilr il<r Hiirtliiire. .Mi>r|ili. .lalirli.. Rami XFI, 



A. r. s. — VOL. xvr. 3(^ 



