1911] Taylor: Mamynah of the 1909 Nevada Expedition. 223 



In studying the characters of our series with the idea of com- 

 paring them with those as given by Allen in the original descrip- 

 tion, only fully adult animals were taken into consideration. 

 The selection of these adults proved to be no small task. The 

 most reliable characters are presented by the skulls. These are 

 the size of the cranium and degree of development of its angles 

 and processes, the transparency of the temporals and frontals 

 (which is more extensive in young animals than in old), and 

 especially the stage of tooth-wear. There is so much variation 

 in these characters, excepting tooth-wear, that, taken individually 

 they can by no means be regarded as conclusive evidences of the 

 age of the animal. The pelage of young animals is more silky, 

 shorter, and brighter than that of adults. The degree of develop- 

 ment of the sexual organs is more misleading than anything else, 

 for sexual maturity is reached quite early, often before the 

 animal is fully adult. Specimens of our series especially illus- 

 trative of this are the following: nos. 7950, 7911, 7929, 7912, 

 7896. In cases in which a given individual of the series could 

 not be said to be fully adult, even though it approximated the 

 adult condition, it was eliminated. 



Reasoning by analogy from chipmunks elsewhere it might be 

 anticipated that those from the higher parts of the mountains 

 would possess characters differentiating them from pictus of the 

 desert flat. The type of Eutamias palmeri C. H. IMerriam 

 (1897c, p. 209) came from an altitude of 8000 feet on Charleston 

 Peak, in southern Nevada. In the above-cited paper Merriam 

 calls attention (p. 190) to the fact that while the sagebrush 

 jilains of the Great Basin are inhabited by Eutamias pictus, other 

 species live in the higher mountains rising from the desert. The 

 Pine Forest JMountains attain an altitude of 9400 feet. The 

 differences between the "mountains" and "plains" series I found 

 to be very slight, as shown beyond. 



With the intention of determining whether there was any 

 local variation in these chipnninks with altitude, adults collected 

 by the Expedition from the sagebrush plain (altitude 4100 feet) 

 and from the mountains above 6000 feet, mostly from 7000 to 

 9000 feet, were segregated and measurements tabulated, with the 

 results shown in the talile of measurements below. Skulls from 



