19161 



Taylor: Beavers of Western North America 



453 



Pig. M. Dorsal view of 

 rostrum, to show 

 method of taking 

 measurement. Ap- 

 proximately one-half 

 natural size. 



Rostra attain greatest breadth in subauratus (measured outside 

 of swellings made laterally by ridge involving maxillary and pre- 

 maxillary bones [see fig. M] ; in subauratus, no. 16383, 34. S mm.; 

 8988, 33.5; 12654, 37.8. In pacificus, no. 3672, 34.9 mm.; 71276, 

 33.6; 71812, 33.4; 71814, 31.7; 78395, 34.5; 87628, 32.7; 87629, 

 34.3. In frondator, no. lid::.! I, 35.5 nun.; :!f>946, 30.2). 



llamular processes of pterygoid hones (see 

 lijj-. K, p. 430) arc broadesl in subauratus 

 (subauratus, no. 16383, 4.1 mm., 8988, 1.2, 

 12654, 4.3; pacificus, no. 3672, 2.1 mm., 

 71812, 2.5, 71814, 2.2, 78395, 3.4, 87628, 2.0, 

 87629, 2.8; frondator, no. 35946, 2.5 mm.). 

 The two juvenals of pacificus from Fisher, 

 Oregon, measure as follows: no. 136605, 4.3 

 nun.; no. 136606, 3.8. The young topotype 



cranium of pacificus from K( helus Lake, 



Washington (no. 126190), has hamulars L3 



mm. broad. The broader hamulars in the 



younger crania of pacificus would seem to 



indicate that this is a character which is different in individuals of 



different ages (see p. 444). 



Mastoid process on the average is closest to auditory bulla in 

 subauratus (see fig. N). Auditory bulla is of somewhat different 

 shape in subauratus than in pacificus or frondator. 



The following comments are in order respecting certain charac- 

 teristics of subauratus as shown by the tallies of measurements, 

 p. 449 and opposite p. 438: 



1 i Tic golden beaver is not, in mosl re- 

 spects, on the basis of all the material, Larger 

 than the canadensis series of heavers. Most 

 of the dimensions of no. 12654 of subauratus 

 are greater than those of the larc-esi skulls 

 of any of the forms tabulated, bowever, ex- 

 cept some of the individuals of its own sub- 

 species shastensis, so that with complete ma- 

 terial a size difference between subauratus 

 and the canadensis series mijrht he proved. 

 (2) Small vertical dimension of the foramen magnum would 

 serve immediately to distinguish skulls of subauratus from those of 

 any other western form of beaver, except in its own subspecies shas- 



Fig. N. Ventral view 

 of mastoid region, to 

 show position of mas- 

 toid process relative 

 to auditory bulla. 

 About one-half nat- 

 ural size. 



