1914] GrinneJl: Mammals and Birds of the Colorado Valley 257 



both external and cranial characters. Scotti, as exemplified by the 

 Colorado River series, has a longer tail, higher ear and paler colora- 

 tion ; the rufous tinges are less bright ; the white endings of the hairs 

 on sides of body and tail and on top of head are more extensive, giving 

 a grizzled effect in the desert race. The skull of scotti is of relatively 

 lighter build; the teeth are smaller, being more slender and hence 

 sharper ; the auditorj^ bullae are more inflated, that Ls, relatively higher 

 and steeper-sided; the rostrum is conspicuously narrower. For 

 measurements of calif ornicus see Dixon (1910, p. 304) and for dis- 

 cussion of relationships see Grinnell and Swarth (1913. p. 373). 



Mephitis estor Merriam 

 Arizona Striped Skunk 



A common species in the riparian strips along both sides of the 

 river. Data pertaining to the eight specimens obtained is given in 

 the accompanying table. This animal evidently does not stray out on 

 to the open desert, being probably kept to the bottomlands by daily 

 need for water; nor has it the physical ability to cover much distance 

 in a night's travel. Those caught were in mesquite, screwbean. willow 

 or arrowweed tracts. Tracks were often seen on the mud at the water's 

 edge. 



A male, no. 10.576, weighed three pounds, two ounces. The female 

 taken near Pilot Knob May 12 contained four foetuses. 



This species of Mephitis is distinctly smaller than M. occidentalis. 

 Although in all of the six skins of estor from the Colorado VaUey 

 there is much more white than in occidentalis, the amount varies indiv- 

 idually to a large extent. In five out of the six there is a white 

 pectoral patch, and in four of the.se there are additional flecks of 

 white mid-ventrally. The longer hairs of the tail are in each case 

 fully white: but a thick gro^vth of relatively short hairs clothing the 

 tail is black terminally, white at base. As the season advances it 

 looks as though the long white hairs of the tail tend to be shed, 

 leading the tail of a darker tone, until the black even predominates. 



The mid-frontal white streak varies in amount, but averages greater 

 than in occidentalis. The dorsal white area {creamy white) is 

 unbroken in no. 10575; in no. 10574 there are tufts of black in the 

 mid-dorsal line over the rump ; in the other four skins there is a 

 well-defined black stripe separating the white into two lateral stripes 



