52 MOSASAURUS. 
Some of the fossil’ specimens show that not unfrequently, while a successional 
tooth occupied a cavity within the fang of its predecessor, it was accompanied by 
another, situated behind the former. For the accommodation of the second suc- 
cessor a cavity was produced, not only at the expense of the fang occupied by the 
first one, but partly at the expense of the alveolar partition and fore part of the 
fang of the functional tooth behind. Figs. 1, ¢, 10, c, Plate X, and Figs. 5, e, 6, e, 
Plate IX, exhibit successive stages in the production of a cavity for a contempo- 
raneous second successional beats The large cavity, represented in the jest figure, 
is evidently compounded of two. 
The pulp cavity of the teeth of Mosasaurus varied in size according to the period 
of development and age of the teeth, but all the fossil specimens I have seen indi- 
cate that it was absent at no period. I have never seen a solid tooth of the Ameri- 
can Mosasaurus, contrary to the statement of Cuvier, in regard to the Maestricht 
Monitor, that the teeth are only hollow during their development, and are most 
frequently found entirely solid. Nor does the large size of the pulp cavity in the 
mature teeth warrant the term of pleodont applied to the Mosasaurus by Owen.’ 
In the shedding of the crowns of the teeth of Mosasaurus they appear generally 
to have been detached from their excavated fangs a couple of lines from the enamel 
border. In several fossil specimens the base of the shed crowns is excavated in 
a conical or lenticular manner from the periphery to the central remnant af the 
pulp cavity. The peripheral border varies from a thin sharp edge to a fractured 
one of a couple of lines in thickness. The remnant of the pulp cavity, where it 
communicates with the excavation, is about a third of the diameter of the crown, 
and from one-third to one-half its length. 
The alveoli generally appear to be completely separated in the ordinary manner 
among most animals by thin osseous partitions. In those instances in which there 
were two nearly contemporaneous successors to a tooth in use, the crowding to 
accommodate the former appears to have been such that the alveolar partition was 
obliterated, and was subsequently replaced by the cylindrical remains of the fangs 
which were excavated for the successional teeth. 
The fossil specimens I have had the opportunity of examining, illustrating the 
dentition of Mosasawrus, are as follows :— 
1. An alveolar fragment, containing a mutilated tooth and the fang of a second, 
from Burlington County, New Jersey, belonging to the museum of the Academy of 
Natural Sciences. It indicates an individual as large as that to which belonged the 
great skull of the Maestricht Mosasaurus, preserved in the museum of the Jardin des 
Plantes of Paris; and the mutilated tooth it contains resembles in its form those in 
advance of the middle of the series in the plaster cast of the skull just mentioned. 
An inner view of the specimen is given in Fig. 1, Plate IX. The fragment is from 
the right side of the upper jaw, and measures about eight inches in length by three 
inches in thickness. The external surface is straight longitudinally and convex 
vertically. About half way between the alveolar edge and the broken border, a 
distance of about three inches, it presents a transverse row of large vasculo-neural 
+ Ossemens Fossiles, Hd. 4, T. 10, p. 134 ; 2 Odontography, 258. 
