MOSASAURUS. 53 
foramina, which communicate with a narrow canal situated just externally to the 
bottom of the fangs of the teeth. 
The mutilated tooth of the specimen (Fig. 1, a) has a large portion of the crown 
destroyed, especially at its outer part, but it has been artificially restored in such a 
manner as sufficiently well to exhibit its original form. 
This agrees with the ordinary descriptions characterizing the teeth of Mosasaurus. 
It is conical, curving moderately backward and inward, and in its perfect condition 
has measured about two inches and a half in length. The diameter at the 
enamelled base has been about fourteen lines, both antero-posteriorly and trans- 
versely. The transverse section is shield-shaped, as represented in the wood-cut 
outlines, Nos. 1, 2, 3, of more perfect specimens of teeth. A pair of acute, feebly 
denticulated, crimped ridges divide the crown irregularly into two surfaces, of which 
the outer is about one-half the extent of the inner. The transverse curve of the 
outer surface forms a short segment of a comparatively large circle, and measures 
at the bottom of the crown fifteen lines; the curve of the inner surface forms 
half an ellipse, and measures twenty-nine lines. Both surfaces have been subdi- 
vided into narrow planes; the outer exhibiting traces of three or four; the inner 
presents eight, of which the extreme ones are twice the width of those inter- 
mediate. 
The fang (Fig. 1, 6) is three inches and three-quarters in length, and is exserted 
about one-fourth; the base of the extra-alveolar portion measuring an inch and 
three-fourths in diameter. The intra-alveolar portion is firmly coossified with its 
alveolus, and is about one-half excavated postero-internally for the accommodation 
of a successional tooth. The cavity, from which the latter has been lost, is open 
at the postero-internal portion of the alveolar border, as represented in Fig. 1, d, 
and is also exposed by the destruction of the thin bottom of the alveolus, as seen 
in the same figure atc. Notwithstanding the extent of the excavation of the fang, 
the pulp cavity of this tooth is not exposed, except through a narrow aperture 
remaining from the canal of communication with the bottom of the fang. 
The next succeeding fang of the fossil (Fig. 1,7) is like that just described, 
except that the cavity for a successional tooth is comparatively small. It is seen 
in the figure at 4, opening at the border of the jaw postero-internally. It is oval, 
about sixteen lines in depth, and eight lines in breadth. The end of the fang is 
seen, as represented in the figure at g, through the open bottom of the alveolus. 
The canal, which usually communicates through the fang with the pulp cavity, is 
filled up with coarse cementum. At the summit of the extra-alveolar portion of 
the fang, from the loss of the crown, the bottom of the pulp cavity of the latter is 
exposed. The aperture is obliquely oval, and measures nine lines in the long 
diameter and six in the short diameter. From the aperture the cavity extends into 
the fang, in the form of a cone, an inch and a half in depth. 
Behind the fang just described, the fossil retains one-half of an alveolus, which 
is interesting, from its exhibiting a thin plate of bone, as seen in Fig. 1, 7, the 
remains of the fang which once occupied it. The plate is coossified with the 
alveolus, and formed part of the wall of the cavity of a successional tooth which 
is lost. 
