No. 4. — Reports on the Scientific Results of the Expedition to 

 the Eastern Tropical Pacific, in charge of Alexander Agassiz, 

 by the U. S. Fish Commission Steamer " Albatross " from 

 October, 1904, to March, 1905, Lieut. Commander L. M. 

 Garrett, U. S. N., Commanding. 



VII. 



Sharks' Teeth and Cetacean Bones. By C. K. Eastman. 



One of the most interesting results of deep-sea dredging in the Pacific 

 is the information that has been gained concerning the distribution of 

 sharks' teeth and Cetacean bones over wide areas of the ocean floor, 

 where, owing to the inappreciable amount of deposition away from the 

 land, it happens that remains of extinct species have lain on the bottom 

 unburied, and are found commingled with those belonging to the modern 

 fauna. Material has now been collected in sufficient abundance, and 

 over sufficiently wide tracts, to acquaint us in the first place with the 

 general facts of distribution, and secondly to furnish data of comparison 

 between fossil and recent forms. A third line of inquiry, which at 

 present can only be suggested, but may possibly be pursued with in- 

 creasing wealth of material, would be a study of the structural modifi- 

 cations which the auditory organs of Cetaceans have undergone since 

 Tertiary times as the result of adaptation to a purely aquatic habitat. 



We may take up first the question of geographical distribution. The 

 most general conclusions that can be drawn from the results of dredging 

 by the "Challenger" Expedition in 1875, and the two "Albatross" 

 Expeditions of recent years (1899-1900 and 1904-1905), are these: — 



1. Teeth of Lanmidae and Carchariidae occur in all parts of the 

 Pacific, but are much more plentiful in southern tropical regions than 

 elsewhere. 



2. Cetacean ear-bones are found only exceptionally north of the 

 equator, but are abundant south of it, especially between parallels 10° 

 and 40° of south latitude. 



