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, c, 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 tooth. The large cavity, represented in the last figure, 

 is evidently compounded of two. 



Ihe 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 docs the large size of the pidp 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 of the 

 pulp cavity. The peripheral border varies from a thin sharp edge to a fractured 

 one of a couple of lines in thicliness. 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 Mosasaurus, 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 skuU 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, Ed. 4, T. 10, p. 134 = Odontography, 258. 



