142 EXTINCT VERTEBRATA FROM THE JUDITH RIVER 
directed from without inwardly. The walls of the cavity are from one to one and a half 
lines thick, and appear quite roughened on their interior surface. 
A transverse section of the crown, about the middle, gives an outline such as is exhi- 
bited in figure 4, a section of the bottom of the crown, as in figure 5, and a section of the 
broken extremity of the specimen, as in figure 6. 
The measurements of this specimen are as follows:—Length of the enamelled surface, 
13 lines; greatest breadth at the lateral angles of this surface, 53 lines; diameter at base 
of crown, from within outwardly, 5 lines; diameter, laterally or antero-posteriorly, 4 lines. 
Three much worn specimens of teeth of Trachodon, (figs. 7—15,) are apparently the 
remains of fangs; the crowns or portions of the teeth faced with enamel having been worn 
away. The specimens have the form of transverse fragments of a parallelogram, with 
concave sides, and with one border bevelled off. The triturating surface (figs. 9, 12, 15,) 
is concave, and presents a slightly elevated crucial ridge, with smaller diverging branches. 
The ridge is of a harder substance than the including dentine, and was no doubt intended 
to preserve a rough condition of the triturating surface as this is worn away. The under 
part of the specimens, (fig. 8 e,) 1s more or less hollowed, apparently from the pressure of 
succeeding teeth. 
The length of the specimens is from 3 to 4 lines; the breadth of the triturating surface, 
from the parallel sides, from 22 to 3 lines. 
Two additional specimens, (figs. 16—20,) found with the preceding, may perhaps beiong 
to a different animal, but it is quite probable also that they belong to a different part of 
the jaws of the same animal. 
One of these specimens, (figs. 18—20,) consists of the crown of a tooth with a small por- 
tion of one side broken away. ‘The crown is a broad four-sided pyramid, with an acute 
summit rising to a short point. The outer surface, as it is presumed to be, is nearly ver- 
tical, devoid of enamel, and elevated into a longitudinal ridge on one side, as represented 
in figure 20. This surface has been slightly roughened, but is worn smooth for part of its 
extent from attrition of an opposing tooth. The inner surface, (fig. 18,) is concave, and 
elevated into a longitudinal ridge, opposite that on the outer surface; besides which, it has 
three short ridges extending from the summit of the tooth. On the unbroken side of the 
specimen, it is likewise embraced by a ridge, curving from the summit to the base of the 
crown. ‘The unbroken side of the latter, (fig. 19,) is triangular, convex, and tuberculated; 
is separated from the inner surface of the tooth by the curving ridge just mentioned; and 
from the outer surface by a ridge, which is transversely notched in the manner of the la- 
teral borders of the teeth of Jyuanodon. Below this side of the crown, the base of the 
specimen presents a sort of osseous envelope or thickening, which becomes obsolete on the 
outer face of the specimen. The base of the crown beneath and on each side is hollowed, 
apparently from the pressure of three successors. 
