FOSSIL FLOKA. 695 



PoPULUS XANTHOLITHENSIS 11. Sp. 

 PI. LXXXV, figs. 1, 2. 



Leaves large, nearly round in outline, but a little broader than long, 

 truncate or slightly heart-shaped at base, rounded above; margin strongly 

 toothed; teeth in lower portion simple and rounded, others, along the side of 

 the blade, inclined to be double-toothed — that is, each large tooth has one or 

 2 smaller rounded projections; petiole long, slender; blade 7 -nerved; cen- 

 tral or midrib strong, straight, pair of ribs nearest the midrib originating 

 at a little distance above the base of the blade, arching around and reach- 

 ing the apex near together, other 2 pairs arising from the apex of the 

 petiole and dividing equally the remaining portion of the blade; midrib 

 with about 3 pairs of secondaries in the upper part, next pair of ribs with 

 4 or 5 branches on the outside, other ribs with numerous branches which 

 anastomose, producing large irregular areas, with minute branches to the 

 teeth; nervilles numerous, mainly broken, occasionally percurrent; finer 

 nervation quadrangular. 



The 2 beautiful specimens figured are the only ones referred to this 

 species. Fig. 1, which lacks the upper portion, is 9.5 cm. broad and 7.5 

 cm. long. It has the petiole preserved for 5.5 cm. Fig. 2, which lacks a 

 portion of one side and a fragment at the apex, is 8.5 cm. in length and 

 10 cm. in width. The petiole is not preserved. 



The relation of this species is evidently with Populus genatrix Newby., 1 

 from the Lower Yellowstone. This is about the same size and much the 

 same shape, except that it is more prolonged at the apex. The margin is 

 described as having "rather small, appressed teeth," while those of P. xan- 

 tholithensis are larger, sometimes double, and never appressed. The former 

 species was described by Newberry as "3-nerved," although the figure 

 shows it to be clearly 5-nerved. The present species is just as clearly 

 7-nerved. The midrib and its branches also differ markedly in the two 

 forms. 



This species has also some affinity with certain of the forms described 

 by Professor Ward from the lower Yellowstone, but the relationship is not 

 close. 



Later Ext. Fl., p. 64; 111. Cret. and Tert. F!.. PI. XII, fig. 1. 



