192 EXTINCT MONSTERS 



rightly considered them to be adapted for swimming, and, 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. 67 and 68. Dr. Mantell was fortunate 

 enough to find, in the year 1820, some vertebra from the English 

 Chalk, near Lewes, which were identified as belonging to a 

 Mosasaurus. It is now known that this reptile attained the 

 length of forty-five feet. 



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 

 Sir Eichard Owen therefore founded upon them the new genus 

 Leiodon. 1 But Leiodon must have been very similar to Mosa- 

 saurus. 



Of late years many fine specimens have been discovered in 

 North America, and the labours of Leidy, Marsh, and Cope have 

 been of the greatest service in completing our knowledge of this 

 strange group of saurians. In the American Cretaceous seas 

 they ruled supreme, as their numbers, size, and carnivorous 

 habits enabled them easily to vanquish all rivals. Probably 

 some of them were seventy-five feet in length, the smallest being 

 ten or twelve feet long. In the inland Cretaceous sea from 

 which the Eocky Mountains were beginning to emerge, these 

 ancient sea-serpents abounded; and many were entombed in 

 its muddy deposits. On one occasion, as Professor Marsh rode 

 through a valley washed out of this old ocean bed, he observed 

 1 Greek leios, smooth, and odous, tooth. 



