RESTORATION OF EXTINCT VERTEBRATES. 1 73 



3. The extreme backward extension of the posterior narcs by 

 the broad union of the palatines. (See Fig. 3.) 



These structures indicate decided differences in habits from those 

 of the modern Hyrax, and so far as they go, point to an aquatic or 

 amphibious mode of Hfe. 



The relationship of Pliohyrax to Hyrax is, however, obvious in 

 the enlarged pair of incisor teeth and in the lophoselenodont 

 structure of the molar teeth, which characters respectively deter- 

 mine its subordinal and ordinal position. 



New and most interesting differences of detail are observed in 

 the dentition : 



1. In Pliohyj'ax the enlarged median incisors are strongly 

 invested with enamel upon the anterior face only. The second and 

 third incisors are both functionally present, and they are separated 

 from the first incisor by a wide diastema, whereas in Hyrax the 

 third incisor has disappeared and the second is a vestigial tooth, 

 found in young specimens just behind the first incisor. 



2. The canine is present as an entirely unique tooth, having 

 two fangs and a complex premolariform crown. 



3. The first, second and third premolars are submolariform, 

 with a flattened outer wall (ectoloph) and more or less complete 

 internal crests. The anterior premolars have therefore less com- 

 pletely transformed into the molar pattern than in Hyrax. 



4. The fourth premolar, however, has a median buttress (meso- 

 style) upon the outer wall (ectoloph), and is thus completely 

 molariform. The third and fourth premolars present an inward 

 and backward cingular extension of the protoloph (see Fig. 3) 

 which may be a specific character. 



5. The molars increase in size posteriorly, and are extended 

 well back behind the junction of the zygomatic arch with the face. 

 (The molar pattern can only be made out in the first superior molar 

 of the right and left sides, in which a prominent mesostyle is seen 

 separating the external lobes, and these are of the lophoselenodont 

 type of PalcBOtherwni and Hyrax.) 



Pliohyrax is thus a very unique animal, quite distinct from 

 Hyrax. It affords us a suggestion of adaptive radiation among 

 members of the order Hyracoidea, hitherto quite unsuspected. We 

 also derive from it a number of clues which may enable us to 

 connect this basal Pliocene representative of the order with still 

 older European or American types. 



Explanation of Plate 2. 



Pliohyrax Kruppii Osborn : Type. After photographs under direction of 

 Professor Eberhard Fraas. 



Fig. I. Side view of type in Stuttgart Museum. 

 Fig. 2. Front view of type. 

 Fig. 3. Palatal view of type. 



Fig. 4. Skull of Dendrohyi-ax arborciis, anterior view. 

 All figures natural size. 



