TjB 



MONOUUAl'US OF NOUTII AMEIllCAN KOUKNTIA. 



Ww. iivciagc of \\\i'. rest, and iiltout ('(|ual.x, (»r rather fulls n little short of, the 

 iiiiiiiniuiii of Icucopits. In length, no fnll-grown .skull of kitcopux drops to 0.90, 

 while the uvcrage of mickigiinenm is only 0.94 ; mid the uvcrnge Icngtli of the 

 under jaw of inichiganensk is similarly just under the miniinuin of leucopus 

 (0.(!0). It is proi)al)l(! that californicus wotild just overreach, on an average, 

 the maxiiiiuni of Iciicopun; hut, with only one specimen before us, we cannot 

 declare this to he so. All the other skulls in the lot fall entirely within the 

 iisuid limits of variation of leucopus jnoper. Here the range is from 0.94 to 

 1.10, as minimum and ma.xiinum, with nn average of barely over 1.00. 

 Tiie zygomatic width of the skulls is just about half their length ; it ranges 

 from 0.45 to 0.57. Tiie height of the skulls, measured as already explained, 

 is about 0.37 ; the length of the lower jaw is about 0.62 ; the interorbital 

 width runs a tritle under 0.20. 



We open the discussion with the examination of a series of eighty-two 

 specimens, collectcil at all seasons in the same locality. This will certainly 

 give us the individual variability of the species, — its normal llexibility, indc- 

 l)endent of those topographic or climatic influences which tend, when opera- 

 tive, to bend it into geographical ditrcrentiation. The measurements are 

 relial)le, at least half of them being taken irom alcoholic specimens; while 

 tile dried skins were prepared with especial care by Mr. Jcnks. Neverthe- 

 less, we shall make lil)eral allowance (see below) for taxidermal defects and 

 other sources of error in calculating our limits of natural variation, as well as 

 in deducing the normal standard of size and proportion of parts. 



'i'Aiii.K \.—iIett»wremenl» of Highly fpecimenii of Hksi'i:komvh lkucopuh, from ilidilkborough, Uatt., col- 



Icclcd by J. IK P. Jenks. 



i {i> 



