248 DURHAM 



North Rim have a dark gray dorsum and face, a tail much darker than 

 the Hancock specimens from the southern Sierra Nevada, California, 

 and the buff reduced in intensity and limited to a fringe along the sides. 



Size: Of the two females taken on the North Rim in early July, one 

 had three 5 mm embryos and the other was in an early stage of pregnancy. 

 The former was considered a subadult, but the latter was fully grown, 

 as was the male, which had 15 mm testes. Comparing these latter two 

 from the North Rim with adults from the southern margin of the range 

 of N. c. acraia, IVIt. Whitney (Hooper, 1940, p. 417) and Charleston 

 Mt. (Burt, 1934, p. 421), we find that they are larger and the sexual 

 dimorphism is greater; e.g., the North Rim female is 96 per cent, 93.5 

 per cent and 72.5 per cent as large as the North Rim male in length of 

 head-body, basilar length of skull and weight, respectively. 



Microtus longicaudus baileyi Goldman 



Habitat: Most of the long-tailed meadow mice from the North Rim 

 were trapped in moist meadows near lakes, streams and springs, but two 

 specimens were taken on a dry forest ridge one-half mile from open 

 water. Nowhere were they found abundant. I considered them scarce in 

 1947 when only two were obtained in four nights of trapping at Tipover 

 Spring, a likely habitat, although seven were taken in one rainy night 

 at Swamp Lake. Two years later none were taken in a night of other- 

 wise good trapping at Swamp Lake, and they then seemed more common 

 in other localities. Apparently their degree of abundance in a given 

 locality may vary widely from year to year. 



Size: In the long-tailed {longicaudus) group of meadow mice the 

 tail usually exceeds one-half the length of head-body. The tails of these 

 meadow mice from the North Rim, as well as those from southeast Utah, 

 average less than one-half (46 per cent) head-body length and, in those 

 populations near the limits of their distribution to the southward, the 

 tails are even shorter. It is evident that a cline of decreasing length of 

 tail in this species (Table 2) occurs from north to south (Map 1). 



