300 PEOCEEDINGS OF THE ACADEMY OF [1888, 



tion, while three of the specimens shown upon the inner face have 

 eight moLirs. As derived from a study of Professor Marsh's collec- 

 tion, the basis of distinction between these genera will depend: 1, 

 upon the numlier of the teeth in the adult condition; 2, upon the 

 presence of a heel, which is apparently wanting in Asthenodon ; 3, 

 upon the presence of one or of two transverse crests connecting the 

 external with the pair of internal cones. 



The name Stylodon is preoccupied, but Amblotherium has the pre- 

 cedence of *S%^acodo?t, (Marsh) and A. soricinum can probably be 

 retained for the larger species with seven molars, thus embracing S. 

 7'obustus with which it agrees closely in measurement. Pkascolestes 

 would then embrace the species with eight molars. But these ques- 

 tions can only be finally determined by a careful revision of all the 

 material. 



It now seems probable that the type maxilla of Kurtodon (IS^o. 

 47755.) fig. 2 a, should be placed somewhere in this series, as held by 

 Owen and not represent a distinct family as maintained by the writer. 

 Since the original study and figuring of the molars, the matrix has 

 been extensively removed, so that the outer faces of the crowns are 

 exposed and show a low antero-internal cusp near the base of the 

 crown ; tliis cusp is very important because it is apparently homol- 

 ogous with the postero-internal cusp of the Amblotherium louver molar. 

 Further, as Mr. Lydekker has ^^ointed out (op. cit., p. 291) the 

 block No. 47786 (S. pudllusf) contains upper molars of a very 

 similar nattern associated with lower teeth, resemblino; those of 

 Stylodon. It is freely admitted that the views before expressed by 

 the writer are not sustained by this additional evidence, although as to 

 the more definite question, it is not as yet evident with which of these 

 jaws the Kurtodon maxilla should be placed. The question will l)e 

 settled by the exposure and study of the crowns of the numerous 

 specimens referred to Stylodon. The Kurtodon crowns are unlike 

 those of Amblotherium soricinum or of Achijrodon since the summit 

 is much broader and the wearing surface, instead of being trenchant, 

 is grinding, as previously described, (op. cit., p. 109). 



Summary. 

 The principle features of the present contribution are the follow- 

 ing: 1, Additional characters of Amphilestes and the probable 

 determination of the premolar-molar formula. 2, Additional char- 

 iicters of Phascolotheriwn, suggesting a division between molars and 

 premolars. 3, A review of the Jm^^Ai^?/^^^ ^^^ntition. 4, The union 



