1897.] NATURAL SCIENCES OF PHILADELPHIA. 487 



horns between males and females in living species of the genera Bos 

 and Bison. A comparison of males and females in old world species 

 of Bos, as B. indicus, B. caffer and B. grunniens, not only confirms 

 the diagnosis of the bovine section of the Bovidce made by Flower 

 and Lydekker : 6 " horns of nearly equal size in both sexes," but 

 shows also the relative position of the horns to the skull and their 

 curvature is subject to no specific sexual variations. In the existing 

 American Bison, to which all the fossil remains of Nearctic species 

 appear more closely related than to the Palearctic species, we have 

 excellent opportunities to determine the sexual characters of the 

 horns from very large suites of specimens in several of our museums 

 as well as among herds of the living animals. Of the latter the 

 author has examined the herd of the Philadelphia Zoological Society, 

 in which about twenty individuals, including six adult females, are 

 represented. Without exception, these females prove that the only 

 difference between male and female bison horns is in the smaller 

 basal calibre of the latter. With respect to curvature and angle of 

 growth from the skull they are singularly like the males in the same 

 herd. With respect to length, the maximum female horn fully 

 equalled the longest of any male horn examined, in this respect 

 showing a length relative to the size of body about 20 per cent, 

 greater than in the male. 7 With respect to the shape of the horn- 

 cores in the two sexes, those of the female are more cylindrical 

 throughout, almost entirely lacking the slightly flattened contour 

 exhibited by the superior surface of male horn-cores. 



It would seem fair to assume, therefore, where there is no evidence 

 to the contrary, that the extinct species of Bos and Bison were anal- 

 ogous to our existing forms in respect to the slight differences be- 

 tween the horns of males and females of the same species, and that 

 marked differences in size and diametric proportions of the adult 

 horn-cores, making due allowance for the more slender and cylin- 

 drical character of the female horn, are diagnostic specific charac- 

 ters. On this basis we will return to a comparison of the horn-cores 

 of the Alaskan skull, No. 13,754, with Cope's type of B. crampianus. 

 The basal processes of the left horn-core of crampianus are wholly 

 wanting, but the contour lines and sulcations of the original parts 

 indicate that but a small portion of the base of the core is missing. 



6 Mam. Liv. and Extinct, 1891, p. 360. 



7 The relative length of sheath to core is greater in females than in males, 

 so that the cores of females average shorter than males of same age. 



