42 MEMOIRS OF THE CARNEGIE MUSEUM 
mentary types, which very often are most exasperating to the student of paleontol- 
ogy, cannot be regarded as finally determining genera and species, and in the pres- 
ent case we must still await the slow process of discovery before a number of questions 
can be satisfactorily determined. The paper here presented can only claim to be 
a report of progress upon our knowledge of this most interesting family, which must 
be regarded as very distantly related to the Suidzx. 
The types of the different genera and species of the family, though sometimes 
very fragmentary, clearly indicate diverging lines. These lines do not possess the 
radical variability met with for instance in the Merycoidodonts (Oreodonts) and the 
Cameloidea, but they are nevertheless of importance, when the conservative charac- 
ters of the family as a whole throughout the lower Oligocene are considered. 
This paper has been considerably delayed by the fact that the writer in the 
early part of the year 1908 was suddenly detailed to take charge of the field-work 
in the Agate Spring Fossil Quarries. The labors in these quarries were rewarded 
with unusually good success, as has been the case every season since they were first 
opened by the Carnegie Museum. Among other important material were found 
a number of portions of individuals of the genus Dinohyus which are of great value, 
as they help to clear up certain anatomical features of that genus which otherwise 
would have been left in obscurity in the present publication. 
For the privilege of study and for aid otherwise given me, I am indebted to Dr. 
W. J. Holland, Director of the Carnegie Museum, at whose request the present work 
was undertaken. ‘To Professors Osborn, Scott, Schuchert, and Lull I am indebted 
for free access to the splendid material of the American Museum of Natural History, 
the Princeton Museum, and the collection of the late Professor Marsh of Yale. ‘To Dr. 
W. D. Matthew of the American Museum, Dr. Witmer Stone of the Academy of 
Natural Sciences, Philadelphia, Mr. J. W. Gidley of the National Museum, Dr. M. 
S. Farr of Princeton University, Professor John C. Merriam, and Mr. E. L. Furlong 
of the California University, and Miss Lucy P. Bush recently of Yale Museum, I here 
wish to extend my thanks and appreciation for important letters and information. 
The excellent series of illustrations in the present paper are mainly due to the 
skilful work of Mr. Sydney Prentice. These illustrations explain many features 
which, without them, would be quite unintelligible. Most of the photographs except 
when otherwise stated, were made by Mr. Arthur 8. Coggeshall. 
Last, but not least, hearty acknowledgment should be expressed to Mr. Andrew 
Carnegie, the founder of the Institute, whose well-known generosity has made it 
possible to carry on the work done both in the field and the laboratory. 
