158 KANSAS ACADEMY OF SCIENCE. 



(B) Horn cores placed at an acute, posteriorly directed angle, with longitudinal 

 axis of skull. 



(a) Circumference of horn cores at base as great as, or greater than, 



length along upper curve. Transverse and vertical diameters 

 about the same. 



1. Horn cores short, recurved, not anywhere arising much 



above occipital crest hison. 



2. Horn cores moderate, strongly and regularly curved up- 



ward and backward occidentalis. 



3. Horn cores moderate, curve regular and moderate, raking 



strongly backward kansensis. 



(b) Circumference of horn cores at base much less than length along 



upper curve. Transverse diameter much exceeding the ver- 

 tical. 



1. Horn cores moderately curved, stout, strongly elliptical in 



cross section crassicornis. 



2. Horn cores strongly curved, elliptical in cross section, moder- 



ately stout alleni. 



(e) Circumference of horn cores at base much less than length upon 

 upper curve. Transverse diameter slightly exceeding the 

 vertical. Curve regular but slight. 



1. Size medium, flattened above ferox^ 



2. Size large, subcircular in section latifrons^ 



The measurements include only the portion of the core covered by 

 horn in the living condition. Transverse diameter is measured par- 

 allel to the longitudinal axis of skull; vertical diameter at right 

 angles to this. 



It must of course be remembered that there is no little individual 

 variation in the form and structure of the horn cores, and also that 

 these organs difPer in the two sexes. These facts introduce real faults 

 in the scheme of classification proposed above, but they appear to be 

 unavoidable. It is a fair question whether any one character offers a 

 more reliable diagnostic value. At any rate, we have to make the 

 best use of available data, and it is unnecessary to point out that due 

 caution should be employed in this particular case. In Bison bison, 

 the form with which we are most familiar, there are marked sexual 

 differences, the horn cores of the bull being much heavier and, as a 

 rule, less curved than in the cow. Probably similar conditions pre- 

 vail among the other species in some measure. It would appear that 

 the specimens upon which species have been founded are generally 

 males, and this fact must be borne in mind. 



The above key contains all the known species of bison found in 

 North America. Of these, there have been found in Kansas the fol- 

 lowing: B. hison, B. occidentalis, B. alleni, B. latifrons, B. kan- 

 sensis. The type specimen of B. alleni was obtained at the Blue 

 river, of this state, and probably the best specimen of B. occidentalis 

 so far secured was obtained from Gove county, and is now in the 



