with Descry § ' s ,,/ Fossil PI \: 



Cretaceous epoch in America, of trees, like, in all tin 



ties of their appearance and economy, those m< imon in 



our present forests. 



In the Miocene plants collected by Dr. Baydenon the Upper 

 Missouri a species of Popvlus occurs I /'. rotundi . which 



exhibits a striking resemblance in general form to that now 

 under consideration. In that species, however, the crenation 

 of the superior margin is uniformly coarser and li and 



the nervation is more delicate. 



Formation and Locality. Lower l i sand 



Blackbird Hill, Nebraska. (Dr. Hayden. | 



FojmiIiis microphvlla. (n. sp.) 



Leaves very small, scarcely an inch in length, roundish 

 line, somewhat wedge-shaped at base, where they arc entire : the 

 upper part of the leaf rounded and deeply toothed, teeth conical. 

 acute or slightly rounded at the summits ; nen es radiating from the 

 base, branching above, the branches terminating in the 

 of the margin. 



This very neat species might be su] i to be onl *m 



of P. elliptica, with which it is iated, but a number 



specimens of each show no shading into each other, and 

 scarcely possible that so wide a variation of marginal di i tal 

 should exist in the same specie-. Although the lei /'. 



elliptica are two or three times as large as th »s • of tl 

 under consideration, the teeth of the margins are 

 the size, and are of a different type, being inclined n] 

 the sides of each tooth of unequal length ; while the 

 of P. microphylla are conical in outline with 

 sides. 



Formation and Locality. Lower < 

 Blackbird Hill, Nebraska. (Dr. Baydi 



Populu*? Debeyana. hi 



A number of leaves in the collection 

 identical with that referred with doubl by Prof. B 



APRIL, 1S6S. 



