18 



NOETH AMERICAN FAUNA. 



[No. 88. 



That these chromatic mutations are inherited in Mendelian ratio 

 among the offspring is strongly suggested in the specimens examined 

 from Point Pelee, Ontario. From the small and somewhat isolated 

 colony of Scalopus inhabiting this locality 25 specimens collected 

 between October 18, 1908, and June 2, 1913, have been examined. 

 Of these specimens 18 have ochraceous patches on the face, while 

 the remaining 7 are normally colored. On purely unsubstantiated 

 evidence, it would appear that "Isick of gray-producing pigment" is 

 here a dominant character, and that the hereditary tendency is 

 probably toward pattern development rather than toward the primi- 

 tive mammaUan monochromatic grayish coloration. 



Mutations of color seem to occur less frequently in Scapanus than 

 in Scalopus; they are most marked in specimens of Scapanus orarius 

 schefferi from Walla Walla and Wenatchee, Wash. Abnormalities 

 in color in the genera Parascalops, Condylura, and NeiirotricJius, are 

 confined to albinistic spots which occur only rarely and usually 

 appear to have been caused by injuries. 



The writer has seen no melanistic specimens of American moles. 



SEXUAL VARIATION. 



The only marked sexual variation in American Talpidse is in size of 

 individuals. This is very noticeable in Scalopus and Scapanus, in 

 which genera males are considerably larger than females. The same 

 condition probably holds in other genera; in the specimens exam- 

 ined of Parascalops, Condylura, and Neurotrichus there is no apparent 

 sexual variation, but this may be due to incorrect determinations 

 of sex. 



AGE VARIATION. 



The most characteristic change in American Talpidae occurring 

 with increasing maturity is a flattening of the skuU and a broad- 

 ening of the base of the rostrum. These tendencies prevail in all 

 genera. Broadenmg of the base of the rostrum is due to lateral 

 thickening of the maxillae. In immature specimens the external 

 roots of the molars are not infrequently exposed in places through 

 the maxiUse. In all genera except Condylura the upper premolars 

 tend to become less cuspidate with increasing age, due not alone to 

 wear of the teeth, but apparently to absorption and physiological 

 processes. 



The genus Condylura furnishes an anomalous and unique age vari- 

 ation; old adults possess a distinct median longitudinal crest on the 

 upper posterior haK of the rostrum. Another peculiar variation 

 accompanying age occurs in Parascalops in which the hair on the 

 nose and tail frequently turns white in old adults. 



