MOSASAUnUS. 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 fines ; 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. l,b) 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 at c. 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. l,/)is like that just described, 

 except that the cavity for a successional tooth is comparatively small. It is seen 

 in the figure at 7i, 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 Avith 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 fossU retains one-half of an alveolus, which 

 is interesting, from its exhibiting a thin plate of bone, as seen in Fig. 1, i, 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 

 b lost. 



