DESCRIPTIONS OF SPECIES. 43 



other parts of the plant shall be obtained before this question can be 

 satisfactorily settled. 



Formation and locality: Cretaceous (Dakota group). Blackbird Hill, 

 Nebraska. 



Populus elliftica Newb. 



PI. Ill, figs. 1, 2. 



Ann. N. Y. Lye. Nat. Hist., Vol. IX (April, 1868), p. 16. 



Fieus ? rhomboideus Lesq. Am. Journ. Sci., Vol. XLVI (July, 1868), p. 96; Ills. 



Cret. and Text. PL (1878), PI. Ill, figs. 1, 2. 

 Phyllites rhomboideus, Lesq. Cret. PL (1874), p. 112, PL VI, fig. 8. 



"Leaves long-petioled, suborbicular or transversely elliptical, slightly 

 cuneate at the base, .and apiculate at summit; lower half of leaf entire; 

 superior half, or more, very regularly and rather finely obtusely sen-ate, or 

 crenate, the points of the teeth inclining upward; primary nerves usually 

 five, sometimes three, radiating from the base at equal angles; from these 

 the secondary nerves spring at acute angles." 



This is an exceedingly neat and well-defined species, very fully repre- 

 sented in Dr. Hayden's collections. It is symmetrical in form, broader than 

 high, forming a transverse ellipse, from the opposite sides of which rise the 

 corresponding and equal projections of the apiculate summit and slightly 

 decurrent base. The crenation of the upper portion of the leaf is very 

 regular and neat, the teeth of small size, and turned upward. The general 

 aspect of the leaf is not very different from that of some specimens of the 

 living P. tremuloides, but the entire margins at the lower half of the leaf, 

 the more elliptical outline, shorter point, and larger and more regular teeth, 

 mark its specific differences with sufficient distinctness, while the corre- 

 spondence which the leaves of the two species present in the general charac- 

 ters of form, nervation, and crenation, affords satisfactory evidence of 

 generic identit}^. 



In the Tertiary plants collected by Dr. Hayden on the upper Missouri 

 a species of Populus occurs (P. rotundifolia), which exhibits a striking resem- 

 blance in general form to that now under consideration. In that species, 

 however, the crenation of the superior margin is uniformly coarser and less 

 acute, and the nervation is more delicate. 



Formation and locality: Cretaceous (Dakota group). Blackbird Hill, 

 Nebraska. 



