S3 Later Extinct floras of North America^ 



any of those with which they are associated and any hitherto 

 described. 



Formation ami Locality. Lignite Tertiary beds. Banks of 

 Yellowstone River. (Dr. Hay den.) 



Popiilus nervosa (n. sp.) 



Var. B. dongata. 



Leaves ovoid or oblong in outline, wedge-shaped at base, 

 abruptly pointed at summit, basal margins entire, sides rather finely 

 toothed, superior margin, coarsely, somewhat doubly dentate ; ner- 

 vation strongly marked, les*s crowded than in var. A.; basal nerves 

 springing from the midrib above the basal margin nearly straight, 

 reaching the sides above the middle and terminating in the first 

 large dentations of the upper margin ; exterior lateral nerves of 

 the basal pair, three or four in number, remote, nearly simple, 

 curved upward, and terminating in the lateral teeth ; secondary 

 nerves above basal pair, three on each side of the midrib, parallel 

 with the basal pair, and connected with them, each other, and the 

 midrib, by numerous strong, generally simple, lattice nerves. 



The nervatiou of these leaves is essentially the same as that of 

 those last described, and which, notwithstanding the difference 

 of ton n that they present, I am inclined to consider as belong- 

 ing to the same species. This diversity of form is not greater 

 than may be seen in the leaves of any poplar tree, and the dif- 

 ferences of dentation are not greater than those observed in 

 different leaves of many living and fossil species. The origin 

 <>f the large basilar nerves above the base of the leaves, the 

 strong ami latticed nervation, and the dentation of the same 

 general character, with the fact that all the specimens are from 

 tin- same locality, all combine to lead me to consider the two 

 forme a- specifically identical. 



Formation and Locality. Lignite Tertiary strata. Fellow- 

 stone River. Nebraska. (Dr. Hay den.) 



1'opillllM .\<*IH*a HOC IK' || (ll. Sp.) 



Leaves long-petioled, 2-:t inches long, ovate, pointed, regularly 

 rounded at the base, coarsely and irregularly toothed, exoept near 



the base, win re the margins are entire; nervation strong, radiating 



