583 ME, M, F. WOOBWAllH ON [May 5, 



cingulum seen in Peralestes is comparable with the similar structure 

 so frequently present in this group, and well exemplified in the 

 upper molars of Talpa. If so, it becomes further evident that the 

 two larger cusps of Peralestes represent the paracone and metacone 

 of these living forms, these cusps being commonly developed quite 

 a long distance from the external border of the tooth (Talpa, fig. 

 35). Consequently the internal shelf, which we have seen in living 

 Insectivores bearing the proto- and hypocoue, is not developed in 

 upper molars of Peralestes. 



If this comparison is correct, we are justified in concluding that 

 the upper molars of this fossil form were not tritubercular in 

 the sense understood by the supporters of the Cope-Osborn theory, 

 and, further, those of Kurtodon being undoubtedly ridged and 

 not tuberculate, while those of IJryolestes and Diplominodon 

 are either undescribed or possess 5 cusps, we consequcjitly have 

 no palteontological evidence to su])port the assumption that u 

 tritubercular stage was passed through by the mammalian upper 

 molar in its evolutions from a protodont or possibly a triconodont 

 tooth. Under these circumstances I see no reason to believe that 

 the primitive cone must necessarily occupy an antero-internal 

 position such as Osborn's protocone does. 



Palaiontological evidence being then wanting or so fragmentary, 

 we are obliged to fall back on the less torn pages of ontogeny. 

 On doing so, we find that the upper molar cusp, which develops 

 first and as a direct continuation of the dentiil germ in the majority 

 of the Mammalia, is the antero-external or paracone : tliis I think 

 is strongly in favour of the view put forward by llcise (19), 

 that the paracone is the most primitive cusp, though I think it 

 would be rather confusing to a]iply Osborn's term " protocone " to 

 it, seeiug that this term has beeu already applied to another cusp 

 in the same tooth. 



Of the primitive nature of the paracone we have slight palccon- 

 tological evidence if, as I have suggested, the largest cone of the 

 Peralestes upper molar (Osborn's protocone) is the homologue of the 

 paracone of living Insectivores. But if we further include the 

 molariform premolars in our study, we find this view is supported 

 both by ontogenists (22) and palaiontologists, for Scott (21 a) has 

 proved, and Osborn and Wortmun (32) have accepted his con- 

 clusions, that the antero-external cone in th(!se teeth is the 

 ])rimitive one from a j>alEeontological standpoint, and Taeker has 

 shown in the Ungulates, and I myself in the Insectivora, that this 

 antero-external cone in the premolars develops first in the onto- 

 geny of the premolar cusps. 



With regard to the tritubercular upper molars of the Centetidce 

 &c. (fig. 34, a & I), I should conclude that the main cone of this 

 type of tooth, usually termed the protocone, was really the paracone: 

 the whole tooth representing only the antero-exteinal triangle of 

 such a form as Talpa (fig. 35, a & I), i. e. the crestentic paracone with 

 its two external cingulum cusps, the two last named being commonly 

 but incorrectly described as the para- and nieta-cone in Centeles : 

 that in the Ceutetidm no marked indications of the protocone 



