50 THE AMERICAN BISONS. 
tween 240 and 275 mm. The lower jaw variés in length in the same series 
from 400 to 420 mm.; the nasals from 194 to 204 mm.; the horn-cores from 
180 to 215mm. The length of the alveolar space of the upper molars varies 
from 138 to 154 mm.; of the lower, from 148 to 165mm. The variation 
in the length of the alveolar space in the females overlaps that of the males, 
the length of the lower molar series ranging from 145 to 158 mm., and that 
of the upper molar series from 136 to 152 mm. It thus appears that in 
respect to the size of the teeth the sexual difference is not very great, — far 
less than that between other parts of the skull and skeleton. 
The individual variation in respect to the horns themselves, in size and 
direction of curvature, is well worthy of special notice. Of two males of 
nearly corresponding ages, one has horn-cores measuring 220 mm. in length, 
the other only 146 mm. ‘The variation in the circumference at the base 
ranges from 235 to 800 mm. In respect to curvature, the horns are some- 
times gently curved the whole length, and sometimes abruptly bent upward 
at the end of the basal third, as shown in Plates V, VI, and VII. They also 
vary greatly in size in individuals of corresponding ages. “The difference in 
these respects between different individuals of Bison americanus is hence much 
greater than the average difference between B. americanus and B. bonasus. 
The variation in the size and shape of the horns resulting from differences 
of age is shown by the series of figures in Plate VIII, where the horn of a 
male of the first autumn, the horn of a yearling male, of a male of four or 
five years, and of a male of twelve to fourteen years, is represented, and also 
two specimens differing greatly in size from about equally aged old bulls. 
Synonymy and Nomenclature. — The first systematic name applied to the 
American bison under the binomial system of nomenclature was Bos america- 
nus, given it by Gmelin in 1788, the specific name being evidently adopted 
from Catesby, who in 1754 called it Bison americanus, as did also Brisson two 
years later. By this specific name, coupled with the generic appellation of 
either Bos or Bison, it has since been almost universally known, a few very 
conservative naturalists having always regarded it as either merely a variety 
of the aurochs or as absolutely identical with it. It hence forms almost the 
only exception among North American mammals of a species that has never 
had a prominent synonym. Hernandez refers to it under the name of 
Taurus mexicanus, ‘but Hernandez wrote long prior to the establishment of 
the binomial system of nomenclature, as did also Nieremburg, who called it 
Taurus q™uivirensis, so that these names have never been regarded as having a 
claim to priority. 
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