570 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxxv. 



animal fares well during the winter months and there is no reason 

 why the woodchuck should not get along equally well. In this 

 instance, and probably in many others, hibernation seems to be a sort 

 of physiological rhythm, similar to sleep, but more prolonged. 



SYNAPTOMYS COOPERI STONEI " Rhoads. 

 STONE LEMMING MOUSE. 



This animal is restricted to fields in which a dense growth of grass 

 is allowed to grow up and remain uncut. One was caught in a live 

 trap on October 5. It was put in a roomy cage and given food and 

 water, but died five days later. 



The lemming mouse breeds as soon as the severe weather of winter 

 is over. A large, round nest of moss and dry grass or sticks is made 

 and the young, usually four or five in number, are brought forth in 

 it. The first of these nests was found March 21. It contained four 

 young, varying considerably in bulk and weight of body, but each 

 having a total length of from 02 to 64 mm. The mother escaped and 

 the young were taken to the house, kept in a room at even temperature 

 and fed milk with a pipette. They seemed to thrive at first, but three 

 days later all died within a few hours. 



The female mates again very soon after giving birth to young. 

 The period of gestation is probably three or four weeks, and if the 

 proeess is kept up all summer, and it doubtless is, the number of 

 young produced by a single female must be not less than twenty or 

 thirty a year. The young of the earlier litters doubtless reproduce dur- 

 ing their first year, and the rate of increase is therefore quite rapid. 



An adult female taken October 5 is grizzled brownish on the back 

 and sides, the hairs being plumbeous at the base and the short fur 

 tipped with bright cinnamon, while the long hairs overlying it are 

 black. Another female taken on March 12 differs from the first only 

 in having grayer cheeks and flanks, and this second specimen is well 

 matched by a male taken the following day. A male taken November 

 •_':') i- much paler, the reddish tips of the hairs being near drab. The 

 feel and >ides are also paler. On the back and rump there is a new 

 growth of short fur similar to the old. A female taken April 12 is 

 similar, but the tail, feet, and sides are even paler than the last speci- 

 men and there is no new growth of fur concealed by the older hairs. 



\ male taken in December has shed the old coat except in the shoulder 

 region and at (lie sides of the belly. The new growth is darker on 

 account of a number of the hairs (in addition to the coarse overfur) 



" Unisons arc given elsewhere (Proc. I". S. Nat. Mus., XXXII, pp. 4G0-461) for 

 adopting this name for the Indiana form of lemming vole. A comparison of the 

 skulls will readily show that it is not gossi, as several nianmialo^ists have sug- 

 gested to the writer. 



