PROFESSOR OWEN ON SOME SPECIES OF THE EXTINCT GENUS NESODON. 307 
mination of this tooth as the first true molar, m i ; and, if the tallying tooth in the 
lower jaw of Nesodon ovinus be referred to, Plate XVI. fig. 7 , m i, it will be seen that 
that tooth would most probably have a longer crown than the successor of d 4 , and 
would most certainly show a more worn-down summit when the fourth premolar had 
come into use in advance of it. These evidences of the nature or homology of the 
fragment of tooth, fig. 18, strengthen my surmise that the teeth (figs. 15-20, Plate 
XVIII.) are all from the same under jaw. 
Plate XVII. fig. 19, is a part of the inner enamelled portion of the crown of a 
molar 3 inches and a half long, including part of a widely open pulp-cavity at the 
base, but with an unknown quantity of the worn or exposed end of the crown broken 
away ; it indicates, therefore, a straight, rootless, molar of considerable length ; but 
the character of the enamel accords so closely with that of the better-defined broken 
teeth above-described, as to indicate it to have belonged to the same genus, species, 
and, probably, individual, as the other teeth with which it was associated. 
The enamel is thinner at its upper broken end than that on the outer side of the 
above-described teeth of the lower jaw? and it becomes still thinner as it approaches 
its lower termination. It forms a nearly flat, long plate, terminating by a free, 
thinned-oflf border on each side along its lower half, where its breadth is from 8 to 10 
lines. The upper half-inch of enamel shows the transverse wavy strise of growth ; the 
next inch is roughened by the punctate impressions and coarser transverse lines : then 
the regular strise of growth are continued for two-thirds of an inch ; and again, the 
punctate character appears for an extent of 3 lines, the alternation of striated and 
punctated tracts continuing to the irregular rugged termination of the enamel plate. 
A thin layer of cement covers the outer surface of the lower part of this fragment, 
which is not plated by the enamel. 
Plate XVII. fig, 20, is a similar but smaller portion of a somewhat larger, long and 
straight tooth, nearly 2 inches in length, and with the enamel-plate 11 lines in 
breadth, terminating on each side in a thin free border. Both upper and lower ends 
of this portion have been broken away, the latter above the pulp-cavity ; and the 
enamel and cement here enclose a solid mass of dentine, of a three-sided shape, one 
of the sides being much narrower than the other two, indicating a long straight 
tooth, thus in proportion to its breadth. The outer surface of the enamel shows the 
same alternation of striated and punctated transverse markings as in the preceding 
fragment. 
As the teeth in the portion of jaw of the Nesodon imhricatus (Plate XVII. figs. 11-14) 
are all of the permanent series, the differences in respect of size which they present in 
comparison with their homologues above-described, are decisive as to their belonging 
to a smaller variety, if not, as is more probable, to a smaller species. That the degree 
of distinction is specific, is further indicated by the punctate markings of the enamel, 
and the more strongly marked strim of growth ; also, by the greater relative thick- 
ness of the teeth of the Nesodon Sulivani, and by their relatively as well as absoliltely 
MDCCCLIII. 2 s 
