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. Man tell was fortunate enough 

 to find, in the year 1820, some vertebrae from the English Chalk 

 near Lewes, which were identified as belonging to a Mosasaurus. 

 In 1 83 1 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. 



Fig. 39. — Lower tooth of Leiodon. i. 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 

 ' Greek — leios, smooth, and odoiis, tooth. 



