1896.] MAMMALIAN DENTITION. 587. 
these have been separated from the lower jaws which Owen described 
under that name and placed in the genus Awrtodon (Athrodon) 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 Diplocynodon (1 ¢, 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. 
Jn 1888 Osborn (16 & 16a) described the upper molars of 
Kurtodon (see ante), Peralestes, Diplocynodon, and also of the Styla~ 
codontia, under which latter head he 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 
Spalacotherium and ot all the Amblotheriide as being trituberculate ; 
evidently he refers Peralestes to Spalacotherium, as suggested by 
Lydekker (10), and Kurtodon to Amblotherium (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 
Peralvstes 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 two internal cusps’, of which the anterior is the largest, 
and a serrated ridge extending along the external border bearing 
several 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 tritubercujar 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 antero-external 
shoulder of his protocone and between this main cone and this 
external paracone, which, to my mind, far better suggests the anterior 
homologue ot the metacone (see Pl. XX VI. 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. 34-36), it appears that the tuberculate external 
? The specimen shows three internal cusps, see fig. 33. 
38* 
