178 PROCEEDINGS OF THE NATIONAL MUSEUM. voi.. 46. 



spects it stands apart from all those with which it was compared. 

 The horn-sheaths and horn-cores are shorter and more strongly- 

 curved. The index of curvature of the horn-sheaths is given as 275.5 ; 

 that of the horn-cores, as 130.8. The latter index is not so small as 

 in some specimens of B. occidentalis, as may be seen below. As shown 

 by the second figure given by Pallas the horns of his specimen sag 

 somewhat strongly as they pass outward, but this may be an indi- 

 vidual variation. 



We may indicate the curvature of the horn-cores of bisons as Tscher- 

 ski has done in the case of the horn-sheaths and horn-cores. The 

 shortest distance between the tip of the horn-core and the base, taken 

 of course on the upper side, is made 100. The ratio of this to the 

 length along the lower curve is then determined. In the case of the 

 type of the species. No. 4157, U.S.N.M., this is 150; in the case of 

 No. 5514, U.S.N.M., it is 140; in No. 2643, U.S.N.M., 142; in the 

 American Museum specimen, it is about 122, according to estimates 

 made from the photograph. Estimated from the figure published 

 by Dr. J. A. Allen * a specimen from St. Michael, Alaska, presents an 

 index of 125. The skull figured by Richardson and described here 

 on page 176 has an index of 127. Here we have a pretty wide varia- 

 tion, a range probably as great as that found in horn-cores of speci- 

 mens of Bison hison. 



Reference has been made on page 162 to LaBaume's paper on which 

 he gives measurements of a number of skulls supposed to belong to 

 Bison priscus. As bearing on the question of the relationship of 

 Bison occidentalis to B. priscus the following statements may be made. 

 We leave out of consideration La Baume's specimen from Marien- 

 burg, as being imperfect and probably not cospecific with the others. 

 The shortest horn-core of five measured by La Baume measured 

 390 mm. along the upper curve and 470 mm. along the lower. The 

 longest horn-core of the six specimens referred in the present paper 

 to B. occidentalis measures 355 mm. along the upper curve, 420 mm. 

 along the lower. With this shorter length there goes a stouter form. 

 In the five skulls of La Baume's list in which may be determined 

 the ratio of the length of the horn-cores along the lower curve, made 

 equal to 100, to the circumference at the base, the ratios, or indices, 

 vary from 57.5 to 71. In the six specimens of B. occidentalis here 

 recorded, the ratios vary from 76 to 86. In the two specimens of 

 B. priscus on wliich the measurement could be made, the distance 

 from tip to tip of the horn-cores was respectively 1,010 and 1,050. 

 In B. occidentalis the measurement varies from 700 mm. to 920 mm. 

 It is evident therefore that the forms included under B. priscus have 

 longer and slenderer horn-cores than do the individuals of B. occi- 

 dentalis. 



1 American Bisons, pi. 4. 



