MOSASAURUS. 67 
the latter, and, indeed, they so far exceed them in relation with the size of the 
mandibular or maxillary teeth that I for a long time hesitated in admitting the 
fragments to belong to the pterygoid bone, and suspected that they belonged to 
part of the upper jaw. ‘The anterior extremity of the larger fragment, however, 
exhibits sutural marks, and the fang of the first tooth indicates this to have been 
smaller than those immediately succeeding it. The second, third, and fourth teeth 
were the largest of the series and nearly equal in size; then followed in size the 
first and fifth, which were nearly equal, and finally the sixth to the eighth, which 
became successively smaller. 
The anterior pair of fangs (Fig. 2, a, b) preserved in the larger fragment are 
coossified with their alveoli, and include in cavities on their inner side posteriorly 
the mutilated remains of successional teeth. Succeeding the fangs indicated there 
is a large vacant alveolus (¢), from which the former occupant has been lost, fang 
and crown together. ‘Then follows a tooth (d), with the end of the crown broken, 
and the fang coossified with its alveolus. 
The tooth, from the broken apex of the crown to the bottom of the fang, is two 
inches and ten lines long. The crown, in shape and construction, resembles those 
described under Nos. 14 and 16, which have only a single acute ridge along the 
posterior or concave border of the crown. ‘The surfaces are devoid of subdivisional 
planes, though there is a slight tendency to their development externally. The 
transverse section is ovate, as represented in the accompanying out- 
line, No. 25. The antero-posterior diameter at the base is nine lines; No, 25. 
the transverse diameter seven lines. ‘The fang on its inner side pre- 
sents a small excavation containing the remains of a successor. 
Back of the tooth described is a vacant alveolus, from which its 
former tenant has been lost, crown and fang together. To the inner 
side posteriorly of this vacant alveolus there is a small cavity for a successional 
tooth which had been destined to occupy the former. . 
Above the fangs of the teeth the bone internally presents a large space or groove 
into which the bottoms of the alveoli for a short distance protrude. 
The two teeth, occupying the small or posterior fragment of the pterygoid bone 
(Fig. 1), are miniatures of the tooth preserved in the anterior fragment, and closely 
resemble the last of the series described under No. 14, and represented in Fig. 5, 
Plate XI. The crown of the foremost of the two teeth has its apex broken, and 
measures at base five lines and a half antero-posteriorly, and four lines and a quarter 
transversely. The crown of the last tooth is half an inch long, four lines and a 
quarter in diameter at base antero-posteriorly, and three lines transversely. 
23. The crown of a small tooth, which has lost its fang, from Burlington County, 
New Jersey, presented to the Academy of Natural Sciences by T. A. Conrad. It 
is represented in Fig. 15, Plate XI, and resembles the crowns of the two teeth last 
described, like them having but a single acute ridge at the back or concave border. 
Its apex is worn off, but in its perfect condition it measured about an inch in length. 
Its ovate base is seven lines and a half in diameter antero-posteriorly, and six lines 
transversely, 
This specimen apparently serves to fix the true character of a similar one obtained 
