16 PROCEEDINGS OF THE ACADEMY OP 



virginiana [and of D. californica\ yet I am unable to establish on 

 them any specific characters. In fact, the variation in the thick- 

 ness and length of the muzzle in different specimens, in addition 

 to other points, are so great, as readily to convey the impression 

 of mail}' more species than really exist." This is certainly true, 

 and, I think, is speaking within bounds. The author's tables of 

 measurements of skulls of D. virginiana show a difference of 

 nearly an inch and a half in total length, in only four specimens ; 

 yet this scarcely represents extremes between the largest old 

 males and the smallest young (though full-grown) females. I 

 have skulls before me upon which a person so minded might 

 base very specious geneiHc characters. The lateral measurements 

 of the skull are variablj^ proportionate to the longitudinal ones. 

 The muzzle is sometimes tumid, at others regularly conic. Some- 

 times the interparietal crest forms a high arch, at others is only 

 a direct backward and upward prolongation of the face. This 

 crest may be only a fourth of an inch, or more than half an inch 

 above the expanded surface of the par'ietals, and when so large 

 it ma}^ be partially detached, appearing like an osseous lamina 

 developed in the fascia separating the masseteric muscles. Gene- 

 rall}", it is in direct proportion to the size and strength of the 

 individual, and is usually smallest in the female. The zj^gomatic 

 arch is very variable in amount of outward curvature. The 

 ramus of the lower jaw may be neai-ly upright, or slope backward 

 so far as to overreach the cond3de. It appears to vary with age. 

 The long lower border of the jaw-bone may form a slight regular 

 curve, or a strong irregular one. In two specimens before me, 

 the difference in total length of this bone alone is a full inch, and 

 the smaller of the two is that of the older animal, as shown by 

 the stronger ridges and deeper depressions for muscular attach- 

 ments, and the much-worn teeth. The difference in length between 

 two canine teeth (both unworn) is a fourth of an inch ; the pos- 

 sessors of these were both adult animals. In general, the tusks 

 of the male are longer and stronger than those of the female. It 

 is unnecessary to cite further details. Elimination of all these 

 and other accidental variations shows how very different a skull 

 should be, to furnish specific characters. 



The length of the tail, compared with the length of the body, 

 appears to have been relied upon in some instances ; but, for 

 several reasons, it is difficult to predicate anything upon this 



[May 2, 



