240 University of California Puhlications in Zoology. [Vol. 7 



measurements) between B. m. megalotis and R. m. deserti. As 

 regards the hind foot, it is a millimeter less than either. The 

 total length of the animal is slightly greater than in either of the 

 two species. This local race is slightly smaller in all three ex- 

 ternal measurements than Reithrodontomys klaniathensis, but 

 in the ratio of length of tail vertebrae to total length accords 

 closely therewith. The same ratio is less in this northern Nevada 

 race than in deserti from California. A slight difference between 

 the two is shown also by the ratio of the length of the hind foot 

 to the total length. 



The most evident feature of the coloration in general is its 

 marked paleness. It is true that specimens of deserti at hand 

 approach it in this respect, but they do not equal it. Klama- 

 thensis, at least as exemplified by the specimens at hand, cannot 

 possibly be confused with the Nevada series because it is so much 

 darker dorsally. Apparently any of our series can be differ- 

 entiated by the general paleness of coloration and short hind 

 foot. 



As to cranial characters (see table of cranial measurements), 

 the rostrum averages slightly narrower than in hiamatJiensis or 

 in longicauda (of which five skulls are at hand) ; the bullae are 

 a little more prominent than in Mamathensis. The skulls, accord- 

 ing to the tabulated measurements, exhibit a tendency to be inter- 

 mediate between Mamathensis and longicauda in size, being larger 

 than the former and smaller than the latter, in the following 

 respects : greatest length, wudth of skull immediately posterior of 

 point of junction with the skull of zygomatic arches posteriorly, 

 and height of cranium at auditory bullae. The tooth row is longer 

 in the Nevada specimens than in either of the other species. 

 There is much variation in cranial charactei*s. Individual 

 examples have the rostrum broad. 



