TllK MAMMALIA OK THE UINTA FORMATION. Tj-l^ 



cluck' tlic variable elements, and asceitaiii those which are constant in the ordinal 

 divisions ; of course, no sharp lines of division, such as wci-e apparent to the oldei- 

 naturalists, exist as we descend in the mammalian series. 



Fii*8t: We observe that while the metapodials play an impoi-tant part in the dis- 

 jMacement, the separate metapodial articulations are not available 

 for taxonomic purposes in the larger divisions above the Protungulata. In 

 the carpus there arc practically but two types of articulation, the "seiial" in the 

 absolutel}' primitive and in some later foi-ms, and the "altornatinp;'' in all but the 

 highly speciaii/ed "adaptively reduced" Aitiodacty la. There are no stages which 

 are of more than family value.* In the tarsus the primitive serial type is i-etained 

 almost nnmodilied in the Proboscidia and Hyracoidea, and in the early equine and 

 Hyrachyus series it passes into the "plane serial," and into the alternating in the 

 Paheosyops series.f The I'emaining Diplarthra show great variation in the mode of 

 metatarsal articulation, so that there is no single type characteiistic of all the genera 

 of the Tapirkhv, or Hhinocerotidai ; Aphelop>i, Acei'athenum, Atelodus and Wiinoceros, 

 each has a different type of metatarsal ai-ticulation. 



Second: In the tarsus Prof. Cope's definitions and principles 

 will not strictly apply, first, because the astragalus extends over the cuboid 

 in some of the earliest and not in some of the more recent Mammalia, and this dis- 

 placement is thus by no means distinctive as between the lower and higher types. 

 The astragalus extends upon the cuboid in one or more members of the " taxeopod " 

 Hyracoidea (Dendrohi/rax) and Condyhwtha (Perijdi/chns), nud in all the Amhly- 

 poda, to a much greater extent than in many of the diplart-hrous Perissodactyla (sec 

 the Equus, Hyrachyus, Paloplotherium series, p. 548). 



As Kiitimeyer points out, thei'c is no parallelism between the diplarthrism oltlic 

 fore and hind feet — diplarthry may be rapidly developed in one while taxcopody per- 

 sists in the other. This arises from the fact that the mechanical problems of adapta- 

 tion to the unguligrade position are dissimilar in the fore and hind feet owing to the 

 ditl'ercnce both in the arrangement of the l)ones and in the motions. Among the Hy- 

 racoidea, Ilijrax is a taxeopod in both feet, while Dendrolnjra.v has a taxeopod manus 

 and diplarthrous pes. In tlie Proboscidia the manus is nearly serial, somelimcH 

 completely so, while the pes is invariably di|)larthrous, although well distinguished 



• Kowiiluvftky'it "(utiptivi; rt'fliiction " nrlsoa intlfpcndcully In llie IJufioilnntii miil ScloiiiKlDnlii. 



\ There are some other mnrkcd lllii<<lmtlrin» of ihi' vuriiihln nntiirc of the poiliiil nrilmlrttlons. Thi; conMucrKT of 

 one or Uie other of the three a8tra);.t1o-eak-anea1 facets is sul)jcct lo speciflc viirintioiis ; rompnri' R. incititui ami /?. Ifp- 

 torhinui (De Blninvillc, Ostco!»r.). Company the aslmgalo-eulioiilal fai'els mi Tiipirut amiruanui m\i\ T. indicuM. The 

 lunar mngntim fiicel ilifTers widely in Etpiui hiirehtlii, tab'iUii* iinil atiniit. 



A. r. s — VOL. XVI. 3s. 



