MAMMALS OF MINNESOTA. 221 



bordering upon the Mississippi river except southwardly, where 

 a variety of our common Geomys bursarius extends into Florida 

 and Georgia and was the first of the family found in the United 

 States though a different species was previously noticed in 

 Mexico. The northern limits of the family are determined by 

 the frosts of winter, for burrowing becomes an arduous task 

 where much of the time the soil is frozen six or more feet deep. 



In the New England and Middle States the family is entirely 

 absent. 



These low-bodied, dense-furred animals are chiefly remarka- 

 ble for the large fur lined pockets extending from the shoulder 

 to the sides of the mouth and opening entirely outside the 

 buccal cavity. The pockets have several special muscles to 

 retain them in place. The pockets are used for carrying food, 

 which in all the species, is stored in subterranean graneries 

 against time of drought or winter frosts. Considerable skill is 

 shown in collecting the proper amount in one place, so that 

 the heat generated in a mass of grass, for example, shall be 

 enough to cause the growth of fresh shoots but not enough to 

 destroy the whole. 



As now understood the pocket-gophers constitute a well cir- 

 cumscribed family of two genera, allied, on the one hand, to 

 the field mice (Arvicolidce) by many important cranial and 

 other characters and, on the other to the pouched mice (Saccom- 

 yidce) by the possession of fur- lined pouches on either side of 

 the mouth (but having no connection with the mucous surfaces). 

 Again, the gophers are allied by quite unmistakable points of 

 agreement with the African mole rats (Georychidce) which in 

 habits they more resemble than either of the above families. If 

 it were pertinent in such a work as this to discuss the relative 

 value of these different affinities, it might be shown that a very 

 good case could be made in favor of a closer relationship with the 

 Georychidce, or Muridce than with the Saccomyidce. After a 

 comparison of cranial characters between Fiber the Sac- 

 comyidce and Geomys it seems well to suggest that the presence 

 oj absence of external pockets ought not to be too implicitly 

 relied upon in collocating the families of rodents. 



It is only safe to say at present that the Geomyidce constitute 

 a distinct family of myomorphic rodents with uncertain inter- 

 ordinal affinities. No definition of the family is necessary in 

 this connection, but the student is referred to the following 

 papers on the group : 



