1915.] 



IN'TEODUCTION. 



25 



soil and an abundant food supply is shown by the development of 

 more robust species under such favorable environment. All the 

 larger species inhabit rich valley bottoms. The smaller are mainly 



B 2048-122 



Fig, 7.— Map showing distribution of certain species and subspecies of Thomomys, and localities at which 



specimens were collected. 



1. apache. 



2. fulvus. 



3. desertorum. 



4. toltecus. 



5. texensis. 



6. haileyi. 



7. mearnsi. 



8. lachuguilla. 



9. cervinus. 



10. sinalox. 



11. chrysonotus. 



12. nigricans. 



13. martirensis. 



14. russeolus. 



15. magdalense. 



16. anitx. 



17. alticolus. 



from deserts where food is scarce and conditions for underground 

 life hard and unfavorable. 



For unknown reasons there is practically no overlapping in range 

 of either genera or species in the family. This may be due to the 



