Xii INTRODUCTORY AND EXPLANATORY 



TWENTY YEARS LATER 



Twenty years have passed since this book was written, 

 and while in that time we have added much to our knowledge 

 of Animals of the Past and added many new and fine 

 examples of them to our museums, the general facts in 

 regard to them remain unchanged. As the stereotyped 

 plates have become worn, and as there seems still a demand 

 for information about u prehistoric" creatures, the time 

 seems opportune to bring some of the chapters down to 

 date, and, especially, to add some new illustrations based 

 on the better and more abundant material now available. 

 Naturally the majority of these cuts have been taken from 

 the rich collections of the American Museum of Natural 

 History which contains more complete specimens of fossil 

 vertebrates than does any other museum. 



Unfortunately the writer is twenty years older than he 

 was and the ideas do not come so quickly, nor the pen 

 record them so readily as of yore. Worst of all, his 

 brain has joined with the labor unions in demanding an 

 eight hour day and refuses to work nights, so when he 

 has most leisure he is least able to avail himself of it. 

 Hence this revision comes at a later date than he had 

 hoped for. 



New York, July 1, 1922. 



