1896.] MAMMALIAN DENTITION. 587\ 



these have been separated from the lower jaws which Owen described, 

 under that name and placed in the genus Kurtodon {Alhrodon) by 

 Osborn (16), who first stated that they were not tuberculate, but now 

 (16 a) apparently regards them as examples of trituberculate molars. 



In America, Marsh (11) has published the briefest note of 

 the discovery of two upper jaws of Dryolestes and a single upper 

 jaw of Biplocynodon (1 c, 8 cheek-teeth) ; these he has not figured, 

 and his descriptions fail to show that they are tritubercular ; in the 

 case of Dryolestes he does not mention the cusps, while in Diplo- 

 cynodon he mentions 5 cusps the arrangement of which does not 

 suggest trituberculy. 



in 1888 Osborn (16 & 16 a) described the upper molars of 

 Kurtodon (see ante), Peralestes, Diplominodon, and also of the Styla- 

 codontia, under which latter head ho places Dryolestes, but on 

 referring to this genus he states that the upper jaw is unknown ! 



In a later work (14) he only mentions the upper molars of 

 Spalacotlierium and of all the Amhlotheriida; as being trituberculate ; 

 evidently he refers Peralestes to Simlacotheriiim , as suggested by 

 Lydol«kcr (10), and Kurtodon to Amhlotherium (Owen). These 

 remarks will show what little material we have upon which to 

 base the existence of the Jurassic tritubercular upper molar which 

 is an essential feature in the tritubercular theory. 



A perusal of Osborn's (16) description of the upper molars of 

 Ferali'stes shows, however, that they are anything but typical 

 trituberculate teeth, for instead of possessing one internal and two 

 external cusps arranged in a triangle, the inner cusp forming the 

 apex, we find ttvo internal cusps ', of which the anterior is the largest, 

 and a serrated ridge extending along the external border bearing 

 ee\eral small cusps ; and as the anterior of these is slightly enlarged 

 Osborn terms it the paracone, calling the two internal cones respec- 

 tively the protocone (anterior) and the metacone (posterior). Now, 

 according to the tritubercular theory, the metacone should be 

 external and in a line with the paracone, not internal in a line with 

 the protocone. Moreover, an examination of Osborn's figure and 

 oF the specimen shows that what he terms the paracone is here 

 developed as an enlargement of the external cingulum and is not 

 in any sense serially homologous with the metacone. 



A comparison of Osborn's two published figures of these teeth 

 shows considerable differences in them, and on examining the actual 

 specimen one finds that the figure in his large monograph (16) is 

 the most accurate, the more frequently copied figure (13) being 

 rather exaggerated in favour of trituberculism ; but with all he 

 seems to have overlooked a small cusp on the autero-external 

 shoulder of his protocone and betvieen this main cone and this 

 external pai'acone,which,tomymind,i'ar better suggests the anterior 

 homologue of the metacone (see PI. XXVI. fig. 33) and consequently 

 the paracone from a tritubercular standpoint, although I believe this 

 tooth to be capable of a totally different interpretation. 



If this tooth be compared with the molar teeth of the living 

 Insectivora (figs. 84-36), it appears that the tuberculate external 

 ' The specimen ebows three internal cuspe, see fig. 33. 



38* 



