12 



ITOETH AMERICAN FAUNA. 



[NO. 39. 



born earlier, and in some regions two litters may be raised. Though 

 I have collected many specimens, I have never seen one younger 

 than the nearly half-grown stage, when they begin to move about, 

 nor have I found specimens of young in any of the museum collec- 

 tions. During July and August many half -grown gophers are 



/ 



3 



B2043-122 



Fig. 2.— Skins of adult females of Thoraomys, showing number and position of mammae in different 

 groups and spe3ie3. (Exact location of nipple indicated by black dot. Relative position of posterior 

 pairs often distorted by method of sewing up skin.) 1, Thomomys umhrinus umbrinus; 2, T. bottx 

 hottse; 3, T.fossor; 4, T.talpoides rufescens. 



caught in traps, but then they are working in the parent burrow 

 or starting new lines for themselves. A little later old and young 

 are in independent burrows. 



The number of young in a litter varies in the different species, as 

 might be expected from the variation in the number of mammae 



