CRETACEOUS REPTILES. 379 
detached teeth and the bones discovered at Hythe did not throw sufficient light, 
at the period of the publication of my ‘ Report on British Fossil Reptiles,’ have 
received some additional elucidation through the unique example of a portion of 
the jaw with one entire tooth in situ and the socket of a second, which was 
discovered in the lower chalk-deposits of Kent, and now forms part of the valu- 
able and instructive collection of Mrs. Smith of Tonbridge Wells. 
On the hypothesis that the series of Saurian bones from the lower greensand 
quarry at Hythe, described in my ‘ Report on British Fossil Reptiles’ (1841, 
p- 157), belonged to the same genus as that founded on the large Saurian teeth 
from the greensand and chalk formations, there was a probability that such genus 
had belonged to the Crocodilian order ; the tibia and fibula and the metatarsal 
bones would favour such a reference, or at least would negative the ascription 
of the Polyptychodon to the Enaliosaurian order. There was a possibility, how- 
ever, that the structure of the head and the mode of fixation of the teeth to the 
jaws might be found to be such as to show the Polyptychodon to have belonged 
to the Lacertian rather than to the Crocodilian order, and to have been, like 
Mosasaurus, the type of an extinct genus of gigantic marine Lizards. The speci- 
men fig. 3. Tab. XXXVIII. inclines the balance in favour of the Crocodilian 
affinities of the remarkable Reptile in question, by showing that the teeth were 
implanted in distinct sockets, not anchylosed to the summits of processes of the 
jaw: the Polyptychodon is thus proved to be a ‘thecodont’ saurian, not an 
‘acrodont’ lizard, like the Mosasaurus : the teeth are also separated by interspaces. 
In fig. 3, the letter b shows the smooth, cement-covered cylindrical base, and c¢ 
the enameled conical crown, with the unequal ridges characteristic of the species 
Polyptychodon interruptus: s is an adjoining vacant alveolus, filled by the chalk 
matrix. 
Order LACERTILIA, Owen. 
Tribe Natantta. 
Genus Mosasaurvs, Conybeare. 
The Mosasaurus was a gigantic reptile, which in some respects more resembled 
the lizard than the crocodile, but had the feet shorter and more adapted for 
swimming. The largest species of Mosasaurus, and that which was first discovered, 
exceeded twenty-five feet in length, and derives its name from the circumstance 
of the locality on the banks of the Meuse, near Maéstricht, where the cretaceous 
deposits abound in which its remains occur. The most perfect skull of the animal 
