DESCRIPTIONS OF SPECIES. 49 



which are generally simple and slightly arched, sometimes broken, and 

 anastomosing with each other. This latter character gives a lattice-like 

 appearance to the leaf, to a degree unusual in the genus." 



Collected by Dr. F. V. Hayden. 



The strong nervation of this species is one of its most marked charac- 

 ters, and has suggested the name given to it, By this and the double den- 

 tation of the superior margin, as well as by their acerine form, these leaves 

 are easily distinguishable from any of those with which they are associated 

 and any hitherto described. 



Formation and locality: Tertiary (Eocene?). Banks of Yellowstone 

 River, Montana. 



POPULUS NERVOSA ELONGATA Newb. 

 PI. XXVIII, fig. 1. 



Populus nervosa var. B. elongata Newb. Ann. N. Y. Lye. Nat. Hist., Vol. IX (April, 



1868), p. 62 ; Ills. Cret. and Tert. PI. (1878), PI. XIII, fig. 1. 



"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; nervation strongly marked, 

 less 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 pah, 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." 



Collected by Dr. F. V. Hayden. 



The nervation of these leaves is essentially the same as that of those 

 last described, and which, notwithstanding the difference of form that they 

 represent, I am inclined to consider as belonging to the same species. This 

 diversity of form is not greater than may be seen in the leaves of any 

 poplar tree, and the differences of dentation are not greater than those 

 observed in different leaves of many living and fossil species. The origin 

 of the large basilar nerves above the base of the leaves, the strong and 



MON XXXV i 



