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osborn: OLIGOCENE, MIOCENE, PLIOCENE EQUID.E. 



Republican River, Northwestern Kansas, 100 feet. 



This horizon contains the advanced rhinoceros Peraceras, also Procamelus, and a small form of Pliauchenia. It 

 includes abundant remains of Pliohippus, Protohippus, Hipparion, Hypohippus, and a number of large and specialized 

 surviving forms of Merychippus, as follows: 



Type of Merychippus republicanus Osborn, 1918.9. Type of Protohippus profectus Cope, 1889.2. 



" " " patruus Osborn, 1918.10. " " Pliohippus nobilis Osborn, 1918.1. 



" " Protohippus rctrusus Cope, 1889.1. 



Snake Creek, Sioux County, Western Nebraska, Matthew, Cook, 1909, Whitford, Matthew, 1916. 



It is remarkable in yielding stages of the Equidse, which are divided by Matthew into two faunal zone groups. This 

 faunal zone grouping may subsequently be found to conform with a geologic grouping, as below: 



1. Fauna of the Merychippus Pockets. 



It is not positively shown that Merychippus, Parahippus, and 

 Hypohippus occur in the pockets containing Protohippus, Hip- 

 parion, and Pliohippus. 



1. Merychippus cf. insignis Leidy. Palates, jaws, teeth, very 

 abundant. 



Diagnosis: — Size small, teeth brachyodont, enamel of 

 lake borders moderately infolded, protocone separate 

 nearly to base, round oval with antero-external fold. 

 Premolar 2 short antero-posteriorly. Lachrymal fossa 

 well defined, not close to orbit. No malar fossa. Feet 

 tridactyl, rather short, slender. 

 Near to M. seversus. 



Smaller than M. sphenodus, teeth shorter, p 2 shorter 

 antero-posteriorly. 



2. Merychippus cf. calamarius. Palates, jaws, and teeth very 

 abundant. 



Diagnosis : — Related to the above but larger and with 

 longer crowned teeth, p 2 of normal proportions. 



3. Merychippus f calamarius propinquus. Equally abundant, 

 with No. 2. 



Diagnosis: — Intermediate between No. 1 and No. 2. 



4. Merychippus Unsignis obliquus, subspec. indesc. A few 

 teeth. 



Diagnosis: — Near to No. 1 but prefossette open or 

 imperfectly closed. 



5. Hypohippus cf. affinis Leidy. teeth and jaw fragments. 



6. Hypohippus pertinax sp. indesc. parts of jaws and teeth. 



Diagnosis: — Size of H. equinus Scott, equally brachyo- 

 dont but pi minute, vestigial (well developed in P. equi- 

 nus), and heel of m 3 more reduced, p-2 slightly broader. 



7. Parahippus cf. cognatus Leidy. Parts of jaws and teeth. 



2. Fauna Partly or Wholly from Later Pockets. 



Occurrence of Merychippus in these pockets is uncertain; they 

 are probably not all of same age. 



1. Protohippus cf. perditus Leidy. Teeth and jaw fragments. 



2. " cf. simus Gidley. " " " 



3. cf. placidus Leidy. " " " " 

 Diagnosis : — Many of the teeth referred to here have 

 much longer crowns and smaller in cross section than 

 the type. 



4. Hipparion cf. gratum Leidy. Teeth and jaw fragments. 



Diagnosis : — Many of the teeth referred to here are 

 much longer-crowned and smaller in cross section. 

 They are separable with difficulty from corresponding 

 variants of P. perditus. 



5. Hipparion cf. occidentale Leidy. Teeth and jaw fragments. 



" sodalis, subspec. indesc. 

 Diagnosis: — Smaller than H. occidentale, protocone 

 flattened oval at base, round oval toward tip. Com- 

 plexity of enamel folding variable, usually less than in 

 H. occidentale, only rarely so simple as in H. whitneyi. 

 Teeth and jaw fragments very abundant. 



6. Pliohippus cf. mirabilis Leidy. Numerous teeth and jaw 



fragments referable to the group, including mirabilis, 

 supremus, pernix, and robustus. 



7. Pliohippus cf. spectans Cope. Many teeth and jaw frag- 



ments referable to the group including spectans, inter- 

 polate, lullianus, etc. 



3. Fauna from Upper Pocket Levels. 



8. Type of Pliohippus leidyanus Osborn. 



Alachua Clays, Archer Beds, Florida. 



This horizon, which may be composite, or of both older and more recent date, namely, of Procamelus-Hipparion age, 

 contains {'t)Tclcoceras protcrus Leidy. In addition to two referred specimens of Hipparion minor the Alachua formation 

 has yielded two equine types, as follows: 



Type of Hipparion ingenuum Leidy, 1885.1. Type of Hipparion plicatile Leidy, 1887. 



The H. plicatile is a highly progressive species. 



4k 



