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 lenticular depression 

 a couple of lines in length, the earliest appearance of a cavity for a successional 

 tooth. This escaped the notice of the artist, and has therefore been inadvertently 

 left out of the figure. The posterior fang (5) 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 MuUica HiU, 

 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, Avhich 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 

 outer of the latter exhibits five planes disappearing beyond the middle 

 of the cro^vn. 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, Avhich has lost its fang, from a Cretaceous formation 

 of Alabama. The specimen was loaned to me by Dr. E. W. Gibbes, who described 

 and figured it in his Memoir on Mosasaurus and the allied genera,^ page 9, plate III, 

 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 croAvn 

 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. II. 



