70 MOSASAURUS. 



They have the same general coustruction 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 imier one, and both are devoid of subdivisional planes. 



The croAvir of the smaller specimen. Fig. 14, has its point slightly bent outwardly; 



externally is nine lines long, with the cvu-vatiu-e of the base thirteen Imes ; the cur- 



A'ature of the base internally is eight lines. The antero-posterior diameter 



No. 30. of i\iQ base is seven lines ; the transverse diameter five lines. The out- 



Oline, 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 yoimg 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 inchided 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 oiiter view is also given in Fig. 9, is a narrow, 



much curved, conoidal crown, about fourteen lines long ; six lines wide at base 



antero-posteriorly, and five lines and a quarter transversely. It is divided 



in the usual manner by a pair of minutely denticulated ridges into two 



surfaces, which are smooth and devoid of subdivisional planes. The 



inner surface more convex and extensive than the outer, presents a cur- 



vatiu-e at base of eleven lines, while the outer ciu-vature measures seven 



lines. The outline. No. 32, represents a transverse section near the base of the crown. 



