PROCEEDINGS OF THE NATIONAL MUSEUM 



VOL. 82 



fore, become important as marking definite stratigraphic horizons. 

 When a sufficient number of such cases come to light, the history of 

 plant species and their migrations can be studied, thereby making 

 identification of new or isolated collections easy and reliable. 



The flora with which the Aspen would immediately be compared 

 is that described by Knowlton * from the overlying Frontier forma- 

 tion. The lists of the two floras are arranged side by side below: 



Sapindopsis schultzi, new species. 



Ficus fremonti Knowlton. 



Ficus? sp. 



Ficris? sp. 



Cinnamomum hesperium Knowlton. 



Cinnaynomum? sp. 



Dryandroides lanceolata KnoM'lton. 



Aralia veatchii Knowlton. 



Staphylea? fremonti Knowlton. 



Dewalquea pulchella Knowlton. 



Phyllites ficifolia Knowlton. 



Phyllites dentata Knowlton. 



Phyllites. 



It will be seen that five species are common to both floras, which 

 is a large percentage when the small size of the floras is considered. 

 So far as the general composition of the floras is concerned, they are 

 very similar and, in my opinion, indicate the same climatic and en- 

 vironmental conditions, namely, a warm temperate and well-watered 

 habitat. Knowlton argues for a tropical or subtropical habitat for 

 the Frontier flora on the basis of several ferns supposed to be related 

 to those now living in such an environment, and on a few species of 

 supposed figs. Studying Knowlton's discussion of the davallioid 



^ Knowlton, F. II., A fossil flora from the Frontier formation of southwestern Wyoming. 

 IJ. S. Geol. Surv. Prof. Paper 108, 1917. 



