253 

 The nieasurciiiLUits of the specimen nre as follows: 



Lill(^S. 



Lcngtli ill the axis 9 



Breadth at tTie upper extremity !) 



Thiclvuess at the upper extremity (> 



Breadth at the lower extremity 8 



Order Ruminantia. 



BISON. 



Bison latifeons. 



Remains of large oxen which were contemporaneous witli the American 

 mastodon have been discovered in several parts of North America. They 

 have been referred to several extinct species, but the materials have been too 

 incomplete to determine the question with any degree of satisfaction whether 

 they pertain to more than one. The fossils indicate individuals very greatly 

 diflfering in size, but the difference is perhaps sexual rather than sjjecific: 

 The more robust specimens probably belonged to males, and the smaller 

 ones to females. 



The most complete specimen which the author has had the opportunity of 

 examining is the cranium, retaining the horn-cores, represented in Figs. 4, 5, 

 Plate XXVIII, one-fifth the natural size. It was discovered by Mr. Calvin 

 Brown and his son Wilfred, of San Francisco, California, while engaged as 

 engineers in the construction of the Spring Valley water-works of that city, 

 and by these gentlemen was presented to the Academy ot Natural Sciences of 

 Philadelphia. Mr. Calvin Brown informs me that tiie cranium was found 

 in a bed of blue clay, 21 feet below the surface, in Pilarcitos Valley. 



The specimen resembles the corresponding part of the skull of the living 

 buffalo {Bison mnericanus) so closely that it will be unnecessary to describe' it 

 in detail. Besides being larger, the horn-cores are especially dispropor- 

 tionately larger, and are more transverse in their direction, or are less inclined 

 backward. The occiput appears proportionately wider and lower from the 

 less degree of prominence of its summit. The latter is, however, ^\•ider, 

 and is more distinctly defined from the posterior occipital surface by the 

 rougher and more prominent protuberance of attachment for tlie nuchal 

 ligament. The occipital foramen is no larger than in the l)uffalo., and the 

 notch below, between the condyles, is more contracted. The Ibrelicad, near 

 its middle, is rather more protuberant than in the bnlfalo. 



