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117 

 UINTA SELENODONTS 



the normal selenodont type, and in the latter the tympanic is hollow. The 

 form of the cannon-bone, when present at all, is characteristic, but, except in 

 the pes of Leptomeryx, the metapodials are not coossified in any of the Eocene 

 or Oligocene genera. In all members of the suborder, without exception, the 

 metapodial keels are confined to the palmar (or plantar) aspect of the bones, 

 but this is equally true of the Tragulina and the earliest Pecora (e.g., Gelocus). 

 The cuboid and navicular are separate in all the genera except Leptomeryx, 

 Hypertragulus, and Hypisodns, as are also the trapezoid and magnum, except 

 in Leptomeryx, and perhaps the other two genera, while in the entire series 

 from the Wasatch onward (assuming that Trigonolestes is properly referred to 

 this phylum) the meso- and ecto-cuneiforms of the tarsus are coalesced. The 

 digital formula varies between V-V and II-II. 



The molars are brachyodont, save for a moderate degree of hypsodontism 

 in the later members of the Camelidce. The premolars are simple, trenchant, 

 and often elongated, but in the more modern Camclida; they become much 

 reduced in size and number. Incisors and canines are usually present in their 

 full number, but Leptomeryx has lost the upper canine and Protoceras all the 

 upper incisors, which in the Camelidce are also reduced, though not entirely 

 suppressed. Except in the main line of the suborder, a very frequent charac- 

 teristic is the conversion of the lower canine into a functional incisor, while 

 the place of the canine is taken by py. More or less obvious indications of 

 this may be seen in the oreodonts, agriochoerids, Lepioreodon, Camclomeryx, 

 Protoceras, and Leptomeryx, and the condition in Protylopus seems to indicate 

 a tendency in the same direction, but the tendency was checked and the true 

 canines were again enlarged. 



It is in the structure of the skull that we find the most characteristic 

 tylopodan features and those which are most constant throughout the sub- 

 order. Riitimeyer's summary needs but little change to apply to the newly 

 discovered forms as well as to those which have long been known. The pre- 

 maxillaries are very complete and reduced only by small incisive foramina. 

 Nevertheless, the skull is distinguished by the very rapid tapering of the face 

 anteriorly, which is expressed particularly in the triangular form of the palate 

 and in the very oblique position of the molar series. The maxillary region 

 of the skull is peculiarly limited, and mainly taken up in the formation of the 

 nasal passage, having but a low alveolus and very limited muscular surfaces. 

 Even the jugal, as well as the lachrymal, takes almost no share in the forma- 

 tion of the face. The infraorbital foramen lies far back, above the last pre- 



