34 University of California Publications in Zoology [Vol. 21 



Lower molars not differing in any essential details from those of 

 califomicus. 



Remarks. — This race probably intergrades with mohavensis along 

 the headwaters of the Mohave River. On the north it probably inter- 

 grades with calif ornicus in Santa Barbara County, though so far no 

 definite area of blending has been found. On the south no locality 

 of occurrence is known below the California boundary line. 



Microtus calif ornicus huperuthrus Elliot 

 Lower California Meadow Mouse 



Arvicola edax, Allen (1893, pp. 184-185). San Pedro Martir Mountains, 



8500 feet. 

 {Microtus) edax, Trouessart (1898-1899, p. 564), part. 

 Microtus calif ornicus huperuthrus Elliot (1903a, p. 161). Type locality 



erroneously given as San Quintin. The real type came from La Grulla. 

 Microtus calif ornicus hyperyllirus, Elliot (1903&, p. 218); and of authors. 



Type specimen. — Male adult ; no. 10740, Field Columb. Mus. ; La 

 Grulla, San Pedro Martir Mountains, Lower California, Mexico: 

 September 10, 1902 ; collected by Edmund Heller. 



Range. — Lower California, Mexico, from San Quintin, on the sea- 

 coast, east to La Grulla and Aguaje de las Fresas, in the San Pedro 

 Martir Mountains. Vertical range, from sea level up to at least 8500 

 feet ; zonal range, from Lower Sonoran to Transition. 



Total number of specimens examined, 7, from the following locality. 

 Lower California, Mexico: La Grulla (Field Columb. Museum), 7. 



Diagnosis. — Size large (hind foot, 24 to 25 mm., condylobasal 

 length of skull in largest individuals, 32.9 mm.) ; second upper molar 

 with or without open posterior lobe ; skull long, lighter than in neglec- 

 tus, and with longitudinal ridges feebly developed even in old adults 

 ( ratio of zygomatic breadth to condylobasal length about 57 % ) ; inter- 

 orbital region not developing single median ridge with age, but always 

 with definite sulcus between ridges. 



Color. — Mass effect of dorsal area ranging from cinnamon-brown to 

 dull Prout's brown, more or less grizzled by the long overhairs. In 

 fresh pelage : Upperparts with light tipped portions of hairs varying 

 from cinnamon-bufP to cinnamon-brown, rather strongly overlaid with 

 long dark Mars brown overhairs. Basal portion of fur everywhere 

 blackish plumbeous. Sides lighter than upperparts. Underparts 

 pallid mouse gray, irregularly darkened by the showing through of 

 the blackish plumbeous hair bases. Anal area nearly pure white. Ter- 

 minal portions of whiskers much lighter than basal portions. Nose 

 lighter and more grayish than region in front of eyes. Ears large, not 

 concealed by fur, with anterior borders covered with light tipped hairs, 

 while posterior borders are nearly naked. Tail bicolor, dark aniline 

 black above and mouse gray below, though the yellow scales often 

 show through. Hands and feet covered with pale mouse gray hairs. 



Skull. — Like that of neglcctus in many respects, but differs in that 

 zygomata are less widely spreading, rostrum relatively shorter and 

 bullae smaller. Dorsal profile considerably flattened, with marked 



