ON THE STRUCTURE AND CLASSIFICATION 
c„s,,s of all the .oolars are ako broken, whreh is ver, improbable. The faet is, 
these eroivns of the molars eoiiskt of elevated anterior and median cusps, followed by a 
low poMcrio,- hed, and with an internal cingulum rising into the low cusp on the inner 
face of the ineilian cusp. When these mutilated crowns are comparetl, one by one, 
with the iierfect crowns of the newly-actpiired jaw (No. 36,822) there can be no 
doubt that they belong to the same pattern. If this be the case, the latter specimen 
is of great interest, as it enables us for the first time to fully characterize the molar 
dentition of Ainplntherium. 
Tliese teeth deserve a somewheat detailed description, (fig. 2). They are seen upon 
the outer surlace, which is devoid of a cingulum. The premolar, which is probably 
closelv resembles pm,, of A. Prevostii (fig. 22, Mes. Mamm.). The crown is bifanged 
and slightly rec■ur^•ed, with a low posterior heel, and a cusp upon the anterior slope, 
which prohablv represents part of the internal cingulum. The molars, in general, dif- 
Fiourf. 2.— .-V portion of the left mandible of the Amphilherium Prevostii, seen upon the outer surface, 
approximately flve times the natural size, from a specimen in the British Museum collection. 
fer from tlio.se of the .1. Prevont'd (fig. 23, Mes. Mamm.), first; in the repression of the 
thinl, or jMi.stcrior cusp, wliicli is replaced by a low, sloping heel ; second, in the elevation 
of the anterior cusp, wliicli rises nearly to the level of the middle cusp; they differ from 
those of A. lirodcripd, lioth in the absence of the posterior cusp and of all tr<ace of a cin- 
gulum ujKin the anterior and posterior slopes of the crown. The molars, as a series, are 
snib-etpial, but the size of the anterior cusp and the width of the posterior heel varies 
somewhat. These teeth, at first sight, approach those of Amhhihermm (PI. IX, fig. 11), 
and l%iMct}lrfites (fig. 1 2), somewhat more closely than those of Amphilestes or Ainphi- 
tf/hiM. 'fhey are, however, widely distinguished from the AmhJotherium molars by the 
promimmee of the anterior lobe, the stout, erect and conical character of the middle 
lolx*, the narrowne,ss of the heel, the strong internal cingulum, and by the sub-equal 
size of the series as a whole. The same features distinguish them from the molars of 
PhaftcoJfMejt, a genus which stands near Amhlotherium, but is distinguished by exter- 
nal cusps.* The separation of this genus from the two following leaves the dental for- 
mida of Amphitheriwn uncertain. 
AMPHITYLUS. 
Amphityi.cs Owexi, gen. et spec. nov.“ 
1 he accompanying cut shows how widely the molars just described differ from 
those of the third specimen referred to AmpMthermm by Professor Owen, viz, the A. 
* It is now probable that Phascolestes belongs to the Stylodon family. 
’ See also abstract, Proc. Phila. Acad., June, 1887. 
