4 PROCEEDINGS OF THE NATIONAL MUSEUM. VOL. 62, 
age. [Excepting the genus Agorophius, the general statement may 
be made that no fossil shark-toothed cetaceans have thus far been 
discovered in North America which are so primitive that they must 
be regarded as probably older than the Miocene. 
As remarked above, the great majority of known squalodonts are 
from deposits conceded to be of Miocene age. On the basis of the 
fauna, as represented by the squalodonts, there is no good reason for 
considering most of the fossil cetaceans derived from deposits in the 
Ashley River region as older than the Upper Miocene. Agorophius 
pygmaeus, apparently, is derived from deposits of Upper Eocene 
age, that is, from the Ashley marl. The age of some of the other 
cetaceans will probably be disputed until some competent geolog st 
obtains additional specimens and reports on their occurrence. 
Our present information regarding this group is chiefly the result 
of accidental discovery of isolated specimens, and our knowledge 
concern ng them should rapidly widen whenever a systematic search 
is made for their remains in marine formations. The fact that 
cetaceans are capable of traveling long distances should place them 
foremost among animals used for correlating widespread deposits. 
They occur not only in typical marine deposits but in estuaries and 
river deltas as well. The main difficulty seems to be a morphological 
one, for we are confronted with the task of determining whether or 
not a species has a long geologic range. Evolution may have been 
and probably was extremely slow in modifying the physical charac- 
teristics of many of the cetaceans. From the evidence afforded by 
fossil cetaceans we see that some of the families have no living 
representatives while some of the genera have made little if any 
progress since the Miocene so far as skeletal characters are concerned. 
The squalodonts represent an archaic group which are still imperfectly 
known and the surviving types probably disappeared before the close 
of the Pliocene. A possible exception to this statement rests on a 
record of a squalodont found in association with quaternary land 
mammals in Italy. 
For the privilege of studying the squalodont material in the Na- 
tional Museum I am indebted to C. W. Gilmore and J. W. Gidley. 
The type of Squalodon tiedemani was intrusted to me for study by 
EK. O. Hovey of the American Museum of National History at the 
suggestion of W. D. Matthew. A collection of cetaceans from the 
Ashley River phosphate deposits, including squalodonts, has been 
placed in my hands for comparison by R. 8S. Lull of Yale University. 
Gerrit S. Miller, jr., has extended facilities for studying the skeletons 
of living cetaceans. W. L. McAtee has verified a reference for me 
at Philadelphia and E. A. Preble has kindly read the manuscript. 
The text figures were drawn by J. R. Malloch and the photographs 
(pls. 1-4) were retouched by Miss Ludwika Wieser. Furthermore 
