MOSASAURUS. 71 
The loosely inserted fangs in advance and behind the one containing the succes- 
sional tooth, appear never to have been coossified with their alveoli. The foremost 
one, in the usual position postero-internally, presents a shallow lentjcular depression 
a couple of lines in length, the earliest appearance of a cayity for a successional 
tooth. ‘This escaped the notice of the artist, and has therefore been inadvertently 
left out of the figure. The posterior fang (>) exhibits a large and conspicuous 
excavation (c). 
The remains of alveoli at the broken ends of the specimen exhibit coossified por- 
tions of fangs, with large excavations indicating them to have been like the one 
preserved with its contained successor. 
This very instructive specimen, in the successive development of the teeth, cer- 
tainly shows that the crown of the new tooth is developed at the postero-internal 
portion of the alveolus, and induces a gradual absorption in the contiguous simply 
inserted fang to accommodate itself. As the crown continues to grow its containing 
cavity enlarges at the expense of the fang of the old tooth, which in the meantime 
becomes coossified with its alveolus as if to strengthen its position or resist expulsion, 
which might indeed readily take place, were it not for the coossification. After the 
new crown has reached its full growth, it is followed by the development of its fang 
which causes the protrusion of the former, while the old fang is reduced to a mere 
chimney or tube bushing or investing the alveolus. 
32. A tooth, which has lost the intra-alveolar part of its fang, from Mullica Hill, 
Gloucester Co., New Jersey, presented to the Academy of Natural Sciences by Dr. 
W.C. Hartman. It is represented in Fig. 16, Plate X ; and has nearly the size and 
form of the successional tooth in the fragment last described. 
The crown, somewhat worn at the apex, is an inch and a quarter long, and about 
six lines and a half in diameter at base antero-posteriorly, and five lines and three- 
quarters transversely. An acute ridge divides it anteriorly, which is not 
perceptibly denticulated ; a posterior ridge is undeveloped, that is to say, No. 33. 
in what appears to be the position it might occupy, there is only a feeble 
elevation like those which subdivide the surfaces of the crown. The Go) 
outer of the latter exhibits five planes disappearing beyond the middle 
of the crown. The inner surface, towards the base, exhibits less dis- 
tinctly nine subdivisional planes. The outline, No. 33, represents a section near the 
base of the crown. 
33. The crown of a tooth, which has lost its fang, from a Cretaceous formation 
of Alabama. The specimen was loaned to me by Dr. R. W. Gibbes, who described 
and figured it in his Memoir on Mosasaurus and the allied genera,’ page 9, plate IIT, 
figs. 6-9, and referred it to an extinct Saurian under the name of Holcodus acuti- 
dens. ‘The specimen, represented in Fig. 17, Plate X, has the enamelled crown 
three-fourths of an inch in length. The base is elliptical in transverse section, and 
measures five lines antero-posteriorly, and four lines transversely. The crown is 
nearly equally divided by acute ridges, which are imperfect in the specimen, but 
appear not to have been denticulated. The surfaces are subdivided into narrow, 
Smithsonian Contributions, Vol. IT. 
