PREFACE 
The preparation of a monograph on the sauropod dinosaurs, which was one of 
the many planned by Professor O. C. Marsh, is now being carried forward by Professor 
H. F. Osborn. At the latter's request, the great type specimen of Barosaurns Marsh 
in the Yale Museum has been fully prepared for study, in order that an adequate 
description of this important genus might be embodied in the monograph. This was 
done during the winter of 191 7, and proved to be a very heavy task even for three 
preparators, but the specimen as thus revealed fully compensates for the labor, since, 
except for the fragmentary character of the limbs, it proves to be one of the finest 
dinosaur skeletons in the possession of the Museum. The study of the material was 
made while the collection was still in the old Peabody Museum building. The vertebrae 
were of necessity boxed for removal and storage, and have since been utterly inacces- 
sible for further reference, hence it has been impossible either to verify or add to the 
measurements on the original bones. If errors have crept into the description, they 
may be in part attributed to this; but it has not been deemed wise to delay publi- 
cation, perhaps for several more years, until the new building is completed and the 
collection installed therein. 
In the preparation of the memoir I have received very material aid from Mr. O. A. 
Peterson of the Carnegie Museum, Pittsburgh, who supplied measurements from the 
type of Diplodocus camegiei, the mounted skeleton of which is there displayed. By 
the American Museum of Natural History, New York City, I was permitted to study 
and measure the exhibited partial skeleton of D. longus described in 1899 by Professor 
Osborn. To Miss LeVene, the executive secretary of the Peabody Museum, I am 
deeply indebted for the preparation of the manuscript and for part of the literary 
research. 
