PROFESSOR OWEN ON SOME SPECIES OF THE EXTINCT GENUS NESODON. 305 
notch, w, this tooth corresponds best with the second premolar {p 2) in the lower jaw 
of the Nesodon imbricatus, fig. 1 1 ; and, the anterior lobe being indicated by its greater 
prominence, it is shown to have come from the right ramus of the jaw. The crown 
has been worn below the part which bears the internal depressions in the N. im- 
hricatus\ and a smooth field of dentine is exposed, with the indented plate of enamel 
on the outer side, and a smooth, slightly convex plate of enamel on the inner side, 
the two plates being interrupted on the anterior and the posterior sides of the crown, 
due apparently to the unequal degrees in which the enamel was extended towards 
the fang along different parts of the crown. The outer coat of enamel is thicker 
than the inner one ; and the former best shows the delicate parallel close-set trans- 
verse striae, indicative of the successive formation of that substance; it is also 
impressed by a transverse row of minute close-set punctations. The fang is enclosed 
by a thin layer of cement, which is continued upon the parts of the crown undefended 
by enamel. The hinder lobe is worn lower than the other, as it is also in the Nesodon 
imbricatus. It differs from the tooth of corresponding form in that species, not only 
in its greater size, as indicated by the dimensions of breadth and thickness, but also 
by the thicker coat of enamel and the greater length of the undivided root. There 
is, also, a worn, smoothly excavated surface on the fore-part of the crown, which 
indicates close contact with an anterior premolar of a different shape from the p 1 in 
the Nesodon imbricatus. 
The length of the enamelled crown here remaining is 10 lines, its breadth 9 lines, 
its thickness 6 lines. 
A portion of the corresponding tooth of the left side of the same jaw is preserved, 
in which the bottom of the enamel-fold is still unobliterated, answering to the island, 
a,p2, fig. 14 , in the second premolar of the Nesodon imbricatus. The length of this 
fragment is 1 inch 9 lines ; its anterior surface shows the same abrasion from pressure 
against the tooth in advance, and the fractured surface exposes a contracted pulp- 
cavity in the crown, which becomes obliterated in the fang. 
The tooth, Plate XVII. fig. 16 , apparently the premolar {p 3), succeeding the one 
last described, is also worn down so near the bottom of the crown, that the inequality 
of the two lobes appears much less than it would be if the same proportion of the 
crown had been preserved as in 3 of the Nesodon imbricatus ; it is probably, there- 
fore, notwithstanding the actual difference in the proportions of the two lobes, the 
tallying tooth. Of the inflected fold of enamel only the bottom of one remains, 
forming an island (a) in the substance of the grinding surface of the crown, opposite 
the angle of the fold, w, indenting the outer surface of the crown. 
The difference in thickness of the outer and inner plates of enamel, which are 
disconnected at the fore and back parts of the grinding surface, is well-marked, that 
of the inner plate being less than that of the insular fold, a. The inner plate termi- 
nates below by a narrow process continued upon the base of each division of the fang. 
The base of the crown begins to divide above the lower boundary of the outer plate 
