1896.] MAMMALIAN DBSTH'ION. 585 



cusp pbylogeny as advanced by the supporters of the Cope-Osborn 

 tritubercular theory. This is a very striking and important fact, 

 and one which will no doubt be considered by trituberculists as 

 strongly supporting their theory, especially as it is generally stated 

 that these trituberculate Insectivores most nearly, amongst living 

 mammals, approach the Jurassic Trituberculata in the character 

 of their molars. This statement is certainly true for the lower jaw, 

 but can be hardly said to hold for the upper molars, there being no 

 resemblance between the teeth of the upper jaw of Oentetes, Ericuhis, 

 and Chrysochlovis ' and those of Peralestes, and only an apparent one 

 with Kurtodon {Stylodon), for Osborn (16) himself states that this 

 latter is not trituberculate but ridged ^ 



Turning now to the first group and examining it in the light of 

 the supposed primitive nature of the protocone, we find here that 

 the upper molar teeth are more complex, possessing 4 or 5 cusps, 

 that the outer cusps (the para- and meta-cones) are more strongly 

 developed than the inner ones ; and in accordance with this we find 

 both these cusps developing before the protocone — an anomalous 

 condition when we remember that the last-named cusp is sup- 

 posed to be the primitive axis of the tooth, the remaining cusps 

 being mere outgrowths from it. Perhaps, if these tnsectivora 

 were the only forms possessed of such a condition, we might agree 

 with Osborn (15) that this is merely a case of accelerated 

 development ; but they are not alone in this respect, for in Man 

 (19), in some Ungulates (22), and in certain polyprotodont 

 Marsupials (20), the paracone invariably develops first, the 

 protocone being either 2nd or 3rd in order of appearance. In fact, 

 in every mammal so far examined, with the exception of the two 

 Insectivores before mentioned, the paracone develops directly from 

 the primitive dental germ and before either the protocone or meta- 

 cone. The constancy of this condition is such that I do not think we 

 can pass over it so lightly as Osborn does, as may be seen from the 

 following quotation (15. p. 503): "In fact the external cusps not 

 only appear before the internal cusp, which palsBontology shows to 

 be the more primitive, but they assume the crescentic form earlier. 

 In other words, their development is accelerated." (Italics mine.) 



If the protocone represents the summit of the original protodont 

 tooth of the ancestor of the Mammalia, it must be the direct con- 

 tinuation of the primitive dentinal germ, and as such should be found 

 to develop in a line with the axis of that structure. That this is not 

 the case is well seen in fig. 32 (PI. XXVI ), where the paracone (s) 

 is found to be identical with the primitive dentinal germ and the 

 protocone (?) appears as a mere internal ledge growing out from 



' Chrysocklorh is trituberculo-sectorial, posBessing a small heel, and not a 

 pure trituberculate as usually stated. Lydekker (10) compares Feralestes and 

 Chrysochloris, but I fail to see the resemblance. 



^ It is very difficult to ascertain Osborn's views regarding Kurtodnn, for in 

 bis large memoir (16. p. 210) he states that there is no real homology between 

 the Kurtodon and CArysoc^forjs dentition, whereas in his additional notes (16") 

 he appears to regard Kurtodon as one of the Trituberculata. 



Proc. Zool. Soc— 189(5, No. XXXVIIl. 33 



