FOSSIL MAMMALIA PROM THE STONKSFIELD SLATE. 427 



the highly developed Carnivora^ and amongst the more spe- 

 cialised Phocidae. These animals possess molars of a perfect 

 Triconodont pattern of obviously secondary origin. 



Another point on which Professor Osborn lays great stress 

 is the origin of the Tritubercular from the Triconodont type 

 by the assumed movement outwards of the protoconid (the 

 median cusp), the paraconid and metaconid occupying the 

 inner angles of the " primitive triangle '' so formed. Phasco- 

 lotherium, Spalacotherium, and Amphitherium represent, 

 according to that author, three stages in the process. How- 

 ever, I can see no traces of the beginning of such a movement 

 in the first species. Spalacotherium has simple tritubercular 

 molars in which the heel is not developed,^ somewhat similar 

 (as observed by Mr. Lydekker, 12) to those of the golden 

 mole, Chrysochloris inaurata, and leading perhaps to the 

 Stylodon type. As for Amphitherium, the molar shows no 

 trace whatever of being more primitive with regard to this 

 supposed movement of the protoconid ; the heel, although not 

 very large, is quite normally developed,^ like that of many 

 other Mesozoic, Tertiary, or recent forms. 



The examination of existing forms only confirms these 

 results : cusps may disappear, and cusps may arise, but the 

 relative position of the protoconid and the two inner cusps is 

 always essentially the same. Embryology also shows that in 

 the development of molars the cusps arise in those positions 

 which they will occupy in the adult tooth (Topinard, 30 ; 

 Rose, 26). 



Mr. W. B. Scott, in a quite recent paper (28), has clearly 

 shown that in the premolars the protoconid remains in place 

 while another cusp, the " deuterocone," is formed on its inner 



' There is no evidence that the teeth of Spalacotherium are of a primitive 

 iuterniediate type, even' should they prove to have been evolved as suggested 

 by Osborn. The angle of the jaw of this genus has always been described 

 as inflected and confluent with the condyle ; one specimen in the British 

 Museum, No. 47,799, shows that it was really separate and little inflected, if 

 at all. 



2 The small cusp figured by Osborn in the molar of Amphitherium in front 

 of the paraconid (17) does not exist in any of the specimens. 



