^^^^ PREFACE "^^^^ 



For assistance in the preparation of this volume I 

 am indebted to many of my colleagues, particularly 

 to Dr. Leland O. Howard, Principal Entomologist 

 (until recently Chief), Bureau of Entomology, Depart- 

 ment of Agriculture; to Dr. William M. Mann, 

 Director of the National Zoological Park and for- 

 merly of the Bureau of Entomology; Dr. Adam B0ving 

 of the Bureau of Entomology; Dr. Waldo L. Schmitt, 

 Curator of Marine Invertebrates, U. S. National Mu- 

 seum; Mr. Charles W. Gilmore, Curator of Vertebrate 

 Paleontology, U. S. National Museum; and Dr. Carl 

 Heinrich, of the Bureau of Entomology; all of whom 

 were so kind as to read the entire manuscript. To 

 Dr. James W. Gidlcy, Assistant Curator of Vertebrate 

 Palaeontology, U. S. National Museum, I am under 

 obligations for checking my statements regarding fos- 

 sil mammals, and for his kindness in verifying my 

 statements concerning the fossils of the Cambrian and 

 immediately following periods I am indebted to Dr. 

 Charles E. Resser, Associate Curator of Invertebrate 

 Paleontology, U. S. National Museum. 



[ix] 



