CHAPTER XTY. 



CONCLUSION. 

 (Plates LIV-LVI, and woodcuts ]47-ir]0, below.) 



The more important characters of the Binocerata, so far as known, 

 have been given in the preceding chapters, and the anatomist can now 

 form a fair picture of characteristic members of the group. It remains to 

 consider what the relations of this peculiar group are to the nearest allied 

 forms, and, especially, to ascertain, if possible, whether the evidence 

 Ijefore us throws any light on the origin of the Duiocerafa, and, more 

 remotely, on the genealogy of all Ungulate Mammals. 



The oldest known mammals are of Triassic age, but the few 

 specimens yet discovered give little information as to the primitive forms 

 of this class. During Jurassic time, mammals were very abundant, and 

 deposits of this age now ofter a promising field for exploration. 



Of Triassic and Jurassic mammals, the author has studied with some 

 care every known specimen in this country, and in Europe, and some of 

 the conclusions here given are based upon this examination. Special 

 attention has been paid to the Jurassic mammals of this country, which 

 the author first discovered in the Rocky IVIountain region. Remains of 

 nearly four hundred individuals, representing many genera and species, 

 have already been secured, and their investigation ])romises to clear up 

 many doubtful points in the early history of this class. 



No Cretaceous manmials are known, and it is this great break in the 

 series of ancient forms that renders any satisfactory clas.sification of the 

 class, living and extinct, at present impossible. 



22 169 



