2 PROCEEDINGS OF THE NATIONAL MUSEUM. VOL. 62, 
compared with those of true squalodonts and our knowledge con- 
cerning it supplemented by the acquisition of the additional material. 
Since Von Meyer’s and Grateloup’s time the group has become 
better known, and its geographic and geologic range widely extended. 
The most important discoveries in regard to the group since 1840, 
as well as the best preserved specimens, have been the anouncement 
of Squalodon antverpiensis by Van Beneden, 1861, Rhizoprion [=Squa- 
lodon] barvensis by Jourdan, 1861, Squalodon bariensis [= zitelli] by 
Zittel, 1876-77, Prosqualodon australis by Lydekker, 1894, and 
Neosqualodon assenzae by Dal Piaz, 1904. 
No records of the occurrence of squalodonts are known to the 
writer from Africa, Asia, or from the Pacific coast of North America. 
This seems rather remarkable in view of the fact that a number of forms 
are known from the Tertiary deposits of Europe, and from similar 
deposits along the Atlantic coast of North America. Other repre- 
sentatives of this group have been found in Patagonia, Australia, 
and New Zealand. This peculiar distribution may be explained in 
part by the inadequacy of our knowledge concerning the Oligocene 
and Miocene marine formations of Asia and Africa. Although con- 
siderable progress has been made in the study of marine inverte- 
brates and land vertebrates of the Pacific coast Province, compar- 
atively little is known concerning its cetacean fauna. 
The possibilities for widespread dispersal of the cetaceans are 
exceptionally great in view of the absence of physical barriers, and 
the chief controlling factor, apparently, is the food supply. It is 
fairly well known that some of the larger cetaceans, especially the 
whalebone whales, perform migrations between definite points. Other 
cetaceans have been observed only in rather limited areas, and a 
few forms are known which are restricted to large fresh-water rivers 
and their estuaries. It is thought that some of the predaceous forms, 
such as the dolphins, follow the routes of the oceanic currents. In 
case of the squalodonts which were, judging from their serrate 
dentition, remarkably well adapted for a predatory life and hence 
could secure an adequate food supply wherever fish or dolphins 
were present in sufficient numbers to insure easy capture, one would 
expect their geographic range to be practically cosmopolitan. Under 
similar prevailing conditions of aquatic life the distribution of the 
squalodonts should have been much the same as that of the Killer 
Whale (Orcinus). 
In the Northern Hemisphere the squalodonts appear in consider- 
able numbers during the Miocene. Their geological history in this 
region previous to the Miocene is unsatisfactory, resting as it does 
upon the occurrence of cetaceans in the Ashley River phosphate 
beds of South Carolina and upon the discovery of an imperfectly 
known squalodont of small size in the Upper Oligocene of Germany. 
