INTRODUCTION 6 



expected to occur between three representative species of 

 their respective subgenera. 



It seems hardly necessary to call attention to the fact that 

 this contribution can lay no claim to completeness. During 

 its preparation many problems were encountered, each of 

 which would well repay months of investigation. But a 

 definite program was laid out and followed, and the work is 

 as comprehensive as was deemed necessary for the special 

 purpose for which it was prepared. 



For reasons explained hereafter, Homodontomys has been 

 arbitrarily selected as the basic type with which to compare 

 first Neotoma, and then Teonoma. 



In the various osteological measurements and percentages, 

 care has been taken to have the individual specimens always 

 follow in the same sequence. 



Material and acknowledgments 



The present investigation was made at the U. S. National 

 Museum under the auspices of the Bureau of Biological 

 Survey of the U. S. Department of Agriculture, and the 

 writer is indebted for the use of facilities and material, 

 consisting of a great quantity of skins and skulls, belonging 

 to both of these. It is also a pleasure to acknowledge 

 indebtedness for the securing or loan of material to the 

 Museum of Vertebrate Zoology through its director. Doctor 

 Joseph Grinnell, and to Messrs. Donald R. Dickey and 

 Laurence M. Huey. For advice he is also under obligation 

 to Doctor Ernst Huber of the Johns Hopkins Medical School. 



Specimens of superior quality preserved in formalin, 

 representing Homodontomys (race macrotis) and Neotoma 

 (race alhigula) were collected in surplus quantity either by 

 the writer or under his direction, and three individuals of 

 Teonoma (race cinerea) by the writer. Upon several oc- 

 casions subsequent to the start of the investigation indi- 

 viduals of the Homodontomys were trapped for special obser- 

 vation of fresh material. 



