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- 
Soot blue shark are shown for comparison. The largest 
tooth im that collection is 53 inches high and 5 inches 
across the base. It takes five teeth of the blue shark to 
fill 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.” There is a technical — and, conse- 
quently, uninteresting — account of Zeuglodon in Vol. 
AXITI. of the “ Proceedings of the United States Na- 
tonal Museum,” page 327. 
Fig. 12. — A Tooth of Zeuglodon, one of the “ Yoke 
Teeth,” from which it derives the name. 
