186 



EVOLUTION OF MAMMALIAN MOLAR TEETH 



horses more closely, because it consists of two halves, a paracone and a 

 metacone, divided by a faint vertical ridge, the mesostyle ; this ridge 

 is much more strongly marked in the extinct genera, mentioned above. 

 It proves that the ancestral types of teeth among the Hyracoidea were 

 lopho-selenodont, like those of Palceoiherium perhaps, the more remote 

 ancestors being sexitubercular and tritubercular. The lower molars 

 exhibit the double crested pattern, similar to that seen in so many 

 Perissodactyla. 



It is an interesting fact that the fossil Hyracoids retain the primitive 

 double rooted canine, a tooth which undoubtedly (see p. 194) once 

 belonged to the premolar series. 



SPECIAL REFERENCES. 



Osborn, H. F., "On Pliohyrax Krupii Osbovn, A Fossil Hyracoid from Sarnos, 

 Lower Pliocene, in the Stuttgart Collection," Proc. Fourth International Congress 

 of Zoology, Cambridge, 1898, pp. 173-174, PI. 2. 



Forsyth Major, C. J., "Pliohyrax grsecus from Samos, :) Geol. Mag., N.S., Dec., 

 IV., Vol. XL, pp. 547-553, Dec. 1899. 



Andrews, C. W., "Notes on an Expedition to the FayAm, Egypt, with Descriptions 

 of some New MammaJs," Geol. Mag., Dec., IV., Vol. X., No. 470, Aug. 1903, pp. 339. 



PROBOSCIDEA. 



The highly complex, plated tooth of Elcphas is so far remote from 

 the molar crown of the general type seen in Protogonodon (Fig. 148) or 



ft or oc. 



a/ fit. 



FIG. 187. Side view of the skull of Pclaoumxtodon Icadnelli, from the Upper Eocene of Egypt. 

 After Andrews. About ^ natural size. 



even in Hcmithlceus (Fig. 138) that it might seem hopeless to attempt 

 to show derivation of the former from the latter ; but the palaeontology 

 of the Proboscidea renders such a connection absolutely certain. 



