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Show 1896.] MAMMALIAN DENTITION. 589 or metacone are as yet visible, while in Chrysochloris (fig. 36.7) the first indication of the protocone has appeared, viz. the internal shelf. This attempt to homologize the main cone of the upper molars of the Centetidce and Chrysochloris with the paracone of other Insectivora is a modification of the view put forward by Mivart in 1868 (12). He regarded the tricuspid triangular crown of the molar teeth of Centetes as a concentration of the eight cusped teeth of Talpa. A n examination of his figures and description will show that he believed the so-called paracone and metacone of Centetes and Chrysochloris to be external cingulum cusps, the main cone of these teeth being formed by a fusion of cones corresponding to the para-and metacones of Talpa, while the protocone and hypocone of the latter he regards as represented by the small internal lobe seen in Chrysochloris1. This view accords in its most important respects with mine, but I do not think that the ontogeny of the trituberculate insectivore molar justifies Mivart's fusion theory, but rather suggests that this tooth corresponds only with the paracone triangle of the Mole's tooth. Such an interpretation would bring these forms into entire accord with the other Insectivores and the Mammalia in general, and we should then find that the cusp which directly continues the dental germ, and consequently is the first to develop, is in all cases homologous, though unfortunately the same name has not been applied to it in all cases. Thus the primitive cone of the upper cheek-teeth of the ancestral mammal finds its homologue in the protocone of the premolar, in the paracone of most molars, but in the protocone of the molars of the trituberculate Insectivores and Peralestes. This has been proved ontogenetically for both the premolars and molars, phylogenetieally also in the former, while in the latter the phylogeny of the primitive cusp is still doubtful. The evolution of the primary cusp of the premolars and molars is now brought into bannony, and it is no longer necessary to suppose that the cusp arrangement of two teeth such as pm. 4 and m. 1, often identical in pattern, have evolved upon different lines. To briefly recapitulate m y conclusions :- (1) The antero-external cone, or paracone above and protoconid below, is the primitive cone both in the molars and premolars. (2) The protocone is borne on an internal shelf of secondary origin (internal cingulum). (3) The metacone is a similar backward development of the paracone, arising very early long before the protocone. (4) The hypocone stands related to the metacone as the protocone does to the paracone. (5) The paracone as the primary cone in the upper molars finds its homologue in the protoconid below2. Unfortunately the cones have been incorrectly lettered in his figure of the upper molar of Chrysochloris, as m a y be seen on reference to his description. A paper by Winge (26) in Danish evidently upholds the same view, viz., that the paracone is the homologue of the protoconid; unfortunately 1 a m unable to read the paper, Plpnv AV» fl»i« ~ „ * 1 but his lettering in his plate and diagrams are very |