UNIVERSITY OF CALIFORNIA PUBLICATIONS 



IN 



ZOOLOGY 



Vol. 12, No. 15, pp. 413-495 March 20, 1916 



THE STATUS OF THE BEAVERS OF WESTERN 



NORTH AMERICA, WITH A CONSIDERATION 



OF THE FACTORS IN THEIR SPECIATION 



BY 



WALTER P. TAYLOR 

 (Comribution from the Museum of Vertebrate Zoology of the University of California) 



CONTENTS 



PAGE 



A. Introduction 414 



I. Evolutionary considerations 414 



II. Details of treatment 415 



B. Material and acknowledgments 416 



C. Nomenclature 417 



D. Changes due to age in a single species (Castor canadensis leucodonta 



Gray) 418 



I. External characters 418 



1. Measurements 418 



2. Coloration and pelage 420 



II. Cranial characters 422 



1. General change 422 



2. Teeth 422 



(1) Milk dentition and the eruption of the teeth 422 



(2) Some characteristics of the permanent dentition 423 



(3) The dental armature as a cutting and grinding 



agency 426 



(4) Parallelism in Castor and Erethizon 426 



3. Dimensions of crania 427 



4. Temporal ridges 427 



E. Description of a new subspecies of beaver from the Cook Inlet region, 



Alaska 429 



Castor canadensis belugae, new subspecies 429 



F. Description of a new subspecies of beaver from eastern Shasta 



County, California 433 



Castor subauratus shastensis, new subspecies 433 



