THE MOSASAURUS. 
213 
increase of the then existing tribes of fishes. From the 
lias upwards, to the commencement of the chalk formation, 
the Ichthyosauri ( ichthus , a fish) and Plesiosauri (_ plesios , 
near to) were the tyrants of the ocean ; and just at the 
point of time when their existence terminated during the 
deposition of the chalk, the new genus Mosasaurus appears 
to have been introduced, to supply for a while their 
place and office, 1 being itself destined in its turn to give 
place to the Cetacea of the tertiary periods. As no saurians 
of the present world are inhabitants of the sea, and the 
most powerful living representatives of this order, viz. the 
crocodiles, though living chiefly in water, have recourse 
to stratagem rather than speed for the. capture of their 
prey, it may not be unprofitable to examine the mechanical 
contrivances by which a reptile, most nearly allied to the 
monitor, was so constructed as to possess the power of 
moving in the sea with sufficient velocity to overtake and 
capture such large and powerful fishes as, from the enormous 
size of its teeth and jaws, we may conclude it was intended 
to devour. 
“ The head and teeth point out the near relations of 
this animal to the monitors ; and the proportions main¬ 
tained throughout all the other parts of the skeleton 
warrant the conclusion, that this monstrous monitor of 
the ancient deep was fivc-and-twenty feet in length, 
although the longest of its modern congeners does not 
exceed five feet. The head here represented measures 
four feet in length ; that of the largest monitor does not 
exceed five inches. The most skilful anatomist would be 
at a loss to devise a series of modifications by which a 
monitor could be enlarged to the length and bulk of a 
grampus, and at the same time be fitted to move with 
strength and rapidity through the waters of the sea ; yet 
in the fossil before us we shall find the genuine characters 
1 Remains of the Mosasaurus have been discovered by Dr. Mantell 
in the upper chalk near Lewes, by Professor Owen in the upper chalk 
of both Kent and Sussex, and by Dr. Morton in the green sand of 
Virginia. 
