44 THE LATER EXTINCT FLORAS OF NORTH AMERICA. 



POPULUS FLABELLUM Newb 

 PI. XX, fig. 4. 

 Boston Journ. Nat. Hist., Vol. VII. (1863), p. 524. 



"Leaves flabellate, orbicular or reniform, obtuse, wedge-shaped at 

 base, slightly decurrent onto the petiole. Margins entire or waved; princi- 

 pal nerves three, two lateral ones reaching nearly to the summit; secondary 

 nerves fine, flexuous, forked." 



There is no living species of Populus of which the normal form of 

 the leaves approaches very closely to that of those under consideration, 

 though one, three-nerved like these, may be occasionally found among the 

 round-leaved poplars. Among the Tertiary plants collected by Dr. Hayden 

 on the Yellowstone is a species, yet unpublished, very much like this, both 

 in the form and nervation of the leaves, and among the Cretaceous plants 

 collected by him in Nebraska is another nearly equally like it; but in both 

 these the upper margins of the leaves are more or less crenulated. 



Formation and locality: Cretaceous (Puget Sound group). Chuckanutz, 

 near Bellingham Bay, Washington. 



Populus genetrix Newb. 

 PI. XXVII, fig. 1. 



Ann. N. Y. Lye. Nat. Hist., Vol. IX (April, 1868), p. 64; Ills. Cret. and Tert. PL 

 (1878), PL XII, fig. 1. 



"Leaves large, cordate in form, acuminate; margins serrate, with rather 

 small appressed teeth; three-nerved; nervation sparse but strong; midrib 

 straight, with few small branches; basilar nerves very strong, given off at 

 an acute angle, much branched at the summit, reaching nearly to the margin 

 far above the middle; from each of the basilar-lateral nerves spring five to 

 six exterior branches, the lower ones very strong and branched, the upper 

 slender and simple." 



In general aspect this leaf is very similar to that of the living P. bal- 

 samifera, and apparently differs from it only in its nervation. It is more 

 decidedly three-nerved than those of any of the living group which it may 

 be supposed to represent — P. balsamifera, P. candicans, P. monilifera, etc.; 

 yet one may occasionally find a leaf of either of these species which in this 

 respect approaches the fossil before us. The dentation of the margin is 



