16 



NOETH AMERICAN FAUNA. 



[No. 38. 



of the molting of tlie ventral parts on the throat and breast; the 

 moltmg areas on the back increase in size and finally enclose each 

 other; the area on the breast works posteriorly, then dorsally; the 

 flanks are the last to molt. The molting process in Neurotriclius, 

 once well begmi, seems to be very rapid, and this may accomit for 

 the sparsity of material of this genus showing molt. 



GEOGRAPHIC VARIATION. 



The maximum of geographic variation occurs in Scalopus and Scapa- 

 nus. In Scolojpus it consists in general of a decrease in size toward 

 the south and an increase in pallor toward the west. The maximum 

 size of individuals is foimd in the north-central part of the range of 

 the genus; the size decreases gradually both to the east and west, 

 and rather abruptly toward the south. The rostrum tends to shorten 

 in the western and southwestern portions of the range. The palest 

 members of the genus are foimd in the region of western Nebraska; 

 the color darkens toward the east and south, becoming somewhat^ 

 ochraceous in the southwestern part of the range. 



The size of Scapanus (except in S. townsendii and S, orarius orarius), 

 like that of Scalopus, decreases toward the south. In the coast 

 region the paUor increases toward the south, and reaches its maxi- 

 mum in specimens of Scapanus latimanus occultus from San Diego 

 County, Cal. ; farther south, however, in the San Pedro Martir moun- 

 tain region of Lower California, the color of Scapanus seems to be- 

 come darker again. In the interior, more mountainous regions, the 

 color of Scapanus becomes darker toward the south, the darkest 

 specimens being from Yosemite Valley, Cal., while the palest are 

 from Crater Lake, Oreg., and the Mount Shasta region, Cal. 



Geographic variation in Neurotriclius manifests itself in a slight in- 

 crease in size and a very slight darkening of color in the southern 

 part of the range. A tendency appears also for the more pronounced 

 development of an anterior cusplike process on the cingulum of the 

 second upper premolar in specimens from the southern half of the 

 range of the genus. 



Geographic variation in Parascalops and Condylura is negligible, 

 though a slightly decreasing size southward is noted in Condylura. 



INDIVIDUAL VARIATION. 



The general size, shape, and proportions of skulls of moles, con- 

 specific and of corresponding maturity, from any given locality are 

 usually constant, variation seldom exceeding more than 4 per cent. 

 On the other hand, the shape of individual cranial bones is noticeably 

 variable, especially that of the interparietai. In a series of specimens 

 of Scalopus from a given locality the posterior border of the palate 



