64 MOSASAURUS. 
of the intra-alveolar portion it exhibits a shallow niche, about five lines long, as a 
commencing cavity for a successor. 
19. The shed crown of a tooth, from Freehold, Monmouth County, New Jersey, 
sent to me for examination from the collection of Dr. C. Thompson, through Prof. 
Cook. It is represented in Fig. 8, Plate IX; is somewhat water- 
worn, and has lost its apex. It resembles the crown of the last de- 
scribed specimen, but is larger and has its surfaces equally divided 
by the anterior and posterior ridges. The diameter of the nearly 
circular base, represented in the accompanying outline, No. 21, is 
ten lines and a half antero-posteriorly, and ten transversely. 
20. A tooth, coossified with its alveolus, from Monmouth County, 
New Jersey, loaned by O. R. Willis, through Prof. Cook. It is represented in Fig, 
10, Plate XI, and is two inches and three-quarters long. 
The crown resembles that of the specimens described under Nos. 16, 17, 18, and 
represented in Figs. 7,9, 11, Plate IX, except that it is more compressed and curved 
in relation with its length. It presents the form viewed as characterizing the genus 
Leiodon, and is about equally divided by the usual pair of ridges into two surfaces, 
which are smooth. The length of the crown is fifteen lines; its 
No. 22. antero-posterior diameter at base ten lines and a half; its transverse 
diaméter seven lines. The transverse section is elliptical, with 
acute poles, as represented in the accompanying outline, No, 22. 
The fang is of unusual breadth, in comparison with its length, 
and is compressed from without inwardly. Postero-internally it 
is deeply excavated, as seen in Fig. 10, c, for the accommodation of a successional 
tooth. 
21. The fragment of a jaw containing two teeth, from Monmouth County, New 
Jersey, presented by Dr. J. H. Slack to the Academy of Natural Sciences. It is 
represented in Figs. 6, 7, Plate XI, and bears a near resemblance to the corre- 
sponding portions of a specimen figured by Dr. Morton ' and loaned to him by Dr. 
De Kay as characteristic of Geosaurus Mitchelli. 
‘The jaw fragment is three inches and a half long, and is broken away along the 
line of the dental canal, at the bottom of the alveoli. Its outer surface is verti- 
cally moderately convex, and presents at the broken border a row of three vasculo- 
neural foramina communicating with the remains of the dental canal. The two 
extremities of the specimen exhibit portions of alveoli, from which teeth appear to 
have been lost together with their fangs. Postero-internally to the portion of the 
anterior alveolus (/) there is an excavation (e) for a successional tooth. 
The intermediate portion of the fragment contains the fang (¢) of a shed tooth, 
coossified with the jaw and containing a successor (d), and an entire tooth (a) occu- 
pying a functional position behind the former. 
The fang (c) of the shed tooth is so intimately coossified with the jaw as almost 
to appear as a constituent portion of the latter. The extra-alveolar portion of the 
fang presents a funnel-shaped excavation or crater, communicating at bottom by 
No. 21. 
1 Synopsis of the Organic Remains of the Cretaceous Group, etc., p. 28, Plate XI, Fig. 10. 
