550 Dr. C. I. Forsyth Major — Flioliyrax from Samos. 



less worn teeth show that in reality the part of the outer wait 

 anterior to the fold mentioned is composed of two cusps, 4 and 1, 

 the part posterior to it, of three cusps, 2, 5, and 3. 



The foregoing statement already partly disposes of the alleged 

 close agreement between upper teeth of hypselodont Hyraces and 

 those of Khinoceridas, which has been repeatedly maintained ; it 

 has even been said that the former have " the same pattern as 

 those of BMnoceros." The Khinoceridae (and Hyracodontidje) were 

 characterized by Cope as having the " anterior exterior crescent of 

 superior molars more reduced." ^ Osborn has more precisely defined 

 this character of Khinoceridae by stating that " the character 

 separating the Ehinoceroses from all other lophodonts is the 

 asymmetry of the external cusps, the metacone being longer than 

 the paracone " ; and he adds besides that the anterior lobe arises 

 from the apex of the paracone, just as the posterior lobe arises from 

 near the apex of the metacone.^ 



A notable difference between the upper molars of Hyracidse and 

 Ehinoceridee is the absence of cusp 2 (mesostyle), and the fusion 

 of cusp 3 with the metacone in the latter,^ which accounts for the- 

 " elongation of the metacone," and the asymmetry of the remaining 

 external cusps. This asymmetry is due besides to the circumstance, 

 that cusp 4 (paracone) projects more outwards than 5, whereas 

 even in those Hyracidse in which 2 becomes fused with 5, na 

 asymmetry is the result. 



I find that the teeth of both hypselodont and brachyodont 

 Hyraces have the same pattern ; the only difference being, as already 

 mentioned, that the outer wall of the former has all the cusps and 

 the intervening folds so reduced that its contour, instead of having 

 the shape of a shallow W, as in the brachyodont teeth, represents 

 a slightly undulated longitudinal line. Besides, there are species 

 of Hyracidje which are semi-hypselodont, being neither brachyodont 

 nor hypselodont.* 



As regards the transverse crests or lobes in the upper teeth of 

 Hyracidse, unworn teeth, whether brachyodont or hypselodont, show 

 each of the two crests incompletely divided into two cusps, the 

 outer smaller ones being apparently the intermediate conules ; these 

 very soon become fused with the inner cusps so as to form the 

 crests. In unworn teeth the inner cusps almost touch the outer 



1 Bull. U.S. Geol. Geogr. Surv., vol. t (1879), p. 228 ; Am. Natur., vol. xiii 

 (1879), p. 771«. 



2 H. F. Osborn, " The Extinct Rhinoceroses " : Mem, Amer. Nat. Hist., ser. i, 

 vol. iii (1898), pp. 87, 88. 



* There is a trace of it in some of the Oligocene Rhinoceroses, as shown ia 

 Osborn's figures of Aceratherium occidcntale and A. tridactylum, op. cit., p. 109. 



* Other characters also, which, like those referred to, have been made use of for 

 dividing the Hyracidaj into two or three genera, prove not to be constant. Thus, 

 a very competent writer, who, as a rule, at least of recent years, is not particularly 

 coy when it comes to the splitting of genera or species, has " come to the conclusion 

 that it is better on the whole to recognize only a single genus for the whole of the 

 Hyraces." (0. Thomas, " On the Species of the Hyracoidea " : P.Z.S. London, 

 1892, p. 52.) 



