124 EVOLUTION OF MAMMALIAN MOLAR TEKTH 



therefore, in these forms, which have been considered typical trituber- 

 culates, the outer cusps are developments of the cingulum, while the 

 main internal cusp has been wrongly termed the protocone and is in 

 reality the paracone, according to Woodward, or combined paracone 

 and metacone, according to Mivart, while the inner cusp (protocone) 

 is greatly diminished in size or lias entirely disappeared. These two 

 authorities, therefore, are agreed on the two points of principal 

 importance regarding Centetes and Erwulus, viz. : (1) the location of the 

 paracone in the main internal cusp and (2) the ultimate loss of the 

 protocone. I strongly concur in these views, for in a series of upper 

 molars, including Potamogale, Solenodon, Centetes, Ericulus, Hemicentetes 

 and Chrysochloris (see Figs. 1-6, PL IV. [our Fig. 69 ]), the stages 

 suggesting the gradual diminishing and final disappearance of the 

 protocone are very complete, amounting almost to demonstration, and 

 there can be little doubt that the molars of the Centetes and Chrysochloris 

 type have been derived from forms similar to that of Potamogale, 

 involving the loss of the protocone. In consequence of this the 

 paracone, or combined paracone and metacone, conies to be the principal 

 inner cusp. In Potamogale [Fig. 69 a, No. 1] the protocone is quite 

 prominent and still typical in form, while in Solenodon [No. 2] it is 

 much reduced and is beginning to divide transversely, or more pro- 

 bably is beginning to separate from a likewise reducing hypocone. 

 This is in favour of the view held by Mivart that the simple inner 

 cusp in Potamogale and like forms is in reality the fused protocone 

 and hypocone. The reduction is carried still farther in Centetes [No. 3], 

 in which two inner cinguliim-like cusps appear, one on each side of 

 the enlarged paracone. In Chrysochloris [No. 6] and Hemicentetes the 

 inner cusp (protocone and hypocone) has entirely disappeared. 



" Regarding Mivart' s ' fusion theory,' I am inclined to believe that 

 Woodward has not given due weight to the evidence cited by Mivart 

 and that there is considerable support for this theory to be found in 

 the modern bats and insectivores. Mivart considered the Potamogale 

 molar as an intermediate form between molars of the Talpa type, 

 having two external triangular prisms, and those of Centetes and 

 Ericulus [No. 4], having only one such prism. He pointed out that 

 in Potamogale there is ' a very interesting approximation of the 

 triangular prisms,' in which the paracone and metacone, although 

 still remaining distinct, are in very close juxtaposition. This view is 

 strongly supported by a series of bat molars to which Mr. G. S. 

 Miller has kindly called my attention. In this series, which includes 

 Vespertilio [No. 7], Seotophilus [No. 8] and Harpioc&phalus [No. 9], are 

 suggested the successive steps from Talpa to Potamogale in the insectivore 

 group. Vespertilio represents the normal or more generalized form, 



