RULERS OF THE ANCIENT SEAS 



69 



beds, specimens may be seen in almost any collection. In 

 the United States National Museum, the jaws of a twelve- 

 foot blue shark are shown for comparison. The largest 

 tooth in that collection is <5f inches high and 5 inches 

 across the base. It takes Jive teeth of the blue shark to 

 Jill the same number of inches. 



The Mosasaurs are described in detail by Professor S. 

 W. Williston, in Vol. IV. of the "University Geological 

 Survey of Kansas.' 1 '' There is a technical and, conse- 

 quently, uninteresting account of Zeuglodon in Vol. 

 XXIII. of the " Proceedings of tlie United States Na- 

 tional Museum,' 1 '' page 327. 



Fig. 12. A Tooth of Zeuglodon, one of the " Yoke 

 Teeth/' from which it derives the name. 



