1912] Grinnell: The Bighorn of the Sierra Nevada 14!) 



corner, whether produced or not, is clearly consequent upon the 

 angularity of the horn at base. The two older rams of sierrat 

 (nos. 13360, 13357) agree in the peculiarity indicated, as com- 

 pared with nelsoni especially of nearly the same age (nos. 10593. 

 1740, 2319, in particular). All of the nelsoni over four years of 

 age and the single cervina, show this distinct triangularity, and 

 the orbital angle is always acute. 



Crania. — The writer has attempted to establish cranial char- 

 acters for the three subspecies of sheep available in the present 

 study. ('. II. Merriam (1901, p. 30) and Elliot (1903, p. 239). 

 especially the former, in describing new races of sheep, point to 

 various cranial features as providing specific characters. The 

 present writer confesses his inability, witli the material in hand, 

 to establish any one cranial character to his satisfaction. He 

 is impressed with the considerable changes in the proportions 

 correlated with increase of the mass of the horn-cores with age. 

 It seems clear that interorbital width, occipital proportions, and 

 other adjacent dimensions must undergo important differential 

 modification with age. And to separate out any character of 

 systematic value would be possible only with very large series 

 of each race, so that the results of individual growth with 

 advancing age could be properly discerned. 



The following are some cranial dimensions of a selected skull 

 of each of the three forms of sheep here treated. As will be 

 seen upon a perusal of the table of general measurements, the 

 first two are nearly of an age. while the last is somewhat older. 

 Age determination, however, is not possible to any close degree 

 of accuracy, especially in the older individuals. 



Si a S3 £ Z £ h'S So £= oi £<no OH 



Una c. nelsoni 1740 249 82.0 51.6 L15.8 100.0 47.6 94.9 50.7 201 



Ovis c. sierrae 103(30 249 SS.6 52.7 122.5 110.6 52.S 95.S 49.7 209 



Ovis c. cervina 437.3 278 85.6 49.6 130.9 120.7 54.4 107.2 61. S 237 



