EDITOR’S PREFACE. 
Soon after Professor Hyatt’s lamented death, January 15, 1902, it 
was the writer’s sad duty, as a representative of the United States Geo- 
ological Survey, to examine all the paleontological collections and manu- 
scripts in Professor Hyatt’s house in Cambridge, in order to take possession 
of those belonging to the Survey. The manuscript of the present volume 
was on his desk and. contains the results of his last work, in which he was 
actively engaged on the day of his death. Fortunately it was almost 
ready for the printer, and although the careful reading of the manuscript 
to determine the author’s exact meaning and intentions has consumed con- 
siderable time, the changes, either in arrangement or in wording, and the 
additions that have been found necessary are very few indeed. These 
changes are all indicated in their proper places by footnotes or bracketed 
statements signed by the editor’s initials, except the unimportant verbal 
b) 
change of “‘Cretacic” to “Cretaceous,” made for the sake of conformity 
with Geological Survey usage. In his recent writings Professor Hyatt 
consistently followed the International Geological Congress rule of ending 
names of all periods and systems with ‘‘ic.” 
The preparation of this work occupied a large part of Professor 
fd 
Hyatt’s time for several years. As early as 1897 a manuscript with the 
same title was submitted to the Director of the United States Geological 
Survey for publication, and soon afterwards the preparation of the illustra- 
tions was begun. A copy of this original manuscript now in my hands 
shows many important differences in arrangement, classification, and 
nomenclature from the later manuscript, indicating that it had been 
thoroughly revised and recast in connection with a restudy of the fossils. 
Although there are some minor inconsistencies, and there would doubt- 
u 
