70 , MOSASAURUS. 
They have the same general construction as the teeth above described, but in some 
respects are peculiar. ‘The crown is demi-conical, curved backward, and divided 
before and behind by acute ridges with obscure traces of denticulation. The outer 
surface, the reverse of the ordinary condition in preceding specimens, is much more 
extensive and convex than the inner one, and both are devoid of subdivisional planes. 
The crown of the smaller specimen, Fig. 14, has its point slightly bent outwardly; 
externally is nine lines long, with the curvature of the base thirteen lines; the cur- 
vature of the base internally is eight lines. The antero-posterior diameter 
No. 30. of the base is seven lines; the transverse diameter five lines. The out- 
CS line, No. 30, represents a transverse section below the middle of the crown. 
The crown of the larger specimen, Fig. 15, has its apex broken off, 
but when perfect was about an inch long. ‘The base is eight lines in 
diameter antero-posteriorly, and five lines and three-quarters transversely. The 
curve of the external surface at bottom is fourteen lines; that of the internal sur- 
face eight lines. The outline, No. 31, represents a transverse section 
near the base of the crown. 
The fang presents the usual characters described in the preceding 
specimens, but the excavation corresponding with the cavity for suc- 
cessional teeth is more median in its position than in the others, as 
represented in Fig. 15, c. 
31. A fragment of the left side of a lower jaw from Monmouth County, New Jersey, 
presented to the Academy of Natural Sciences by Charles C. Abbott. It is apparently 
from the fore part of the mandible of a young Mosasaurus, and is of special interest 
because it contains the fangs of three teeth, of which one is firmly coossified with its 
alveolus, while the others are loosely inserted. The specimen, from which the inner 
part of the bone has been removed to exhibit the fangs of the teeth, is represented 
in Fig. 8, Plate XI. 
The fragment of jaw is five inches in length, and at its middle is an inch and 
three-quarters in depth. Its outer surface forms about one-third of a cylinder, and 
just above the middle presents a row of four large vasculo-neural foramina, com- 
municating with the dental canal, which pursues its course exterior to the bottoms 
of the included fangs of the teeth. A row of smaller foramina exists also near the 
base of the fragment. Near the alveolar border, opposite the posterior of the con- 
tained fangs, the jaw is an inch and a quarter thick. ‘The inner side of the base, 
as seen in the figure, exhibits the sutural marks for the splenial bone. 
The coossified fang of the specimen is intermediate to the others, and is nearly 
half excavated to accommodate a successor which it still retains, as seen in Fig. 8, d. 
The successional tooth, of which an outer view is also given in Fig. 9, is a narrow, 
much curved, conoidal crown, about fourteen lines long; six lines wide at base 
No. 31. 
tomes 
antero-posteriorly, and five lines and a quarter transversely. It is divided 
No. 32. in the usual manner by a pair of minutely denticulated ridges into two 
@F surfaces, which are smooth and devoid of subdivisional planes. The 
inner surface more convex and extensive than the outer, presents a cur- 
vature at base of eleven lines, while the outer curvature measures seven 
lines. The outline, No, 32, represents a transverse section near the base of the crown. 
