No.1.] 



COPE ON HORIZONS OF EXTINCT VERTEBRATA. 



53 



In conclusion, it may be observed tliat the lacunae in the series as pre- 

 sented by one continent render us dependent on the other for the evidence 

 necessary for the complete elucidation of the laws of the creation of ani- 

 mal life. Phylogenies can be thus constructed which would otherwise 

 be impossible, and the results of researches into the earliest types of 

 Vertebraia become intelligible. Thus I have been able to prove, in suj)- 

 port of a thesis published in 1874, that the earliest Ungulate Mammalia 

 were pentadactyle and plantigrade. I have also shown that the ankle- 

 joint had not, in the primitive Mammalia.; the hinge-like character that 

 it has in the later ones, but that it is without the interlocking superior 

 articulation. The small size of the brain of early Mammalia., already 

 pointed out by Lartet, has received extensive confirmation by the re- 

 searches of Marsh, who has also shown the progressive increase in size 

 of the whole body in various Mammalian hues. To these results I now 

 add another, which is derived from the study of numerous Permian Yer- 

 tehrata, viz, that the earliest land vertebrates had a persistent chorda 

 dorsalis. 



COMPARISON WITH THE SCALE DERIVED FROM PAX, GEOBOTANY. 



I now consider another kind of relation presented by the American 

 and European horizons. I allude to the florae, for my knowledge of 

 which I am necessarily dependent on the labors of others. I first ex- 

 hibit the determinations of the ages of the American formations akeady 

 discussed, made by Mr. Lesquereux on the basis of the vegetable re- 

 mains which they contain. I place by the side of these my own deter- 

 minations of the ages of the same beds, as already related. The former 

 are derived fi?om the full memoir of Mr. Lesquereux in the Annual Eeport 

 of the United States Geological Survey of the Territories for 1872, pp. 

 410-417. It will be observed that there is a constant discrej)ancy between 

 the two tables. 



If the determinations of Mr. Lesquereux be correct,* it is evident from 

 the above that the vegetable life of North America reached its present 

 condition one epoch or period earlier than the higher Vertehrata, and 

 that the nomenclature is thus thrown back by so much. It would ap- 

 pear that the recent flora of North America is a period older than the 



* The above parallels are well presented by Dr. Peale in liis report to Dr. Haydcn, 

 Ann. Rept. U. S. Geol. Surv. Terrs. 1874, p. 141 et seq. 



