138 EXTINCT MONSTERS. 
with his usual foresight, concluded that this monster was a marine 
reptile of great strength and activity, having a large tail flattened 
vertically and capable of being moved from side to side with 
such force and rapidity as to be a powerful organ of propulsion, 
capable of stemming the most agitated waters. The large conical 
recurved teeth, the largest of which was nearly three inches long, 
are well seen in Figs. 37 and 38. Dr. Mantell was fortunate enough 
to find, in the year 1820, some vertebre from the English Chalk 
near Lewes, which were identified as belonging to a Mosasaurus. 
In 1831 a portion of a lower jaw with large conical teeth was 
discovered in the Chalk near Norwich. But these teeth were not 
quite similar to those of the Maestricht specimen, and Professor 
Owen therefore founded upon them the new genus Leiodon.’ 
But Leiodon must have been very similar to Mosasaurus. 
Fic. 39.—Lower tooth of Letodon. 1. Side view. 2. Profile. 
Of late years many fine specimens have been discovered in 
North America, and the labours of Leidy, Marsh, and Cope have 
1 Greek—/ezos, smooth, and odous, tooth. 
