DESCRIPTIONS OF SPECIES. 51 



resemblance of the group to the leaves of the poplars is strong enough to 

 warrant their provisional association. 



Among the fossil leaves which have been described as species of Populus 

 some of the many forms of P. mutdbilis Heer show a considerable resem- 

 blance to these before us, and one phase of Populus leucophjlla Ung. (Fl. 

 Gleichenberg, p. 177 [21], PI IV, figs. 6-9), especially that represented in' 

 fig. 9 of the plate cited, could hardly be distinguished from some of the 

 Bridge Creek leaves 



Formation and locality : Tertiary (Miocene). Bridge Creek, Oregon. 



Populus khomboidea Lesq. 

 PI. XX, figs. 1, 2. 

 Am. Journ. Sci , Vol. XXVII (1859), p. 360. 



In the collection of the Northwest Boundary Commission are numerous 

 specimens which I have referred with some doubt to species of Populus 

 described by Lesquereux. My specimens are, however, too imperfect to 

 permit me to decide with certainty the question of their identity. Asso- 

 ciated as they are with Inoceramus, there can be no reasonable doubt of 

 their Cretaceous age. 



Among the fossil leaves brought from Orcas Island, there are some 

 which bear considerable resemblance to these, but they are too imperfect to 

 render the comparison satisfactory. 



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

 Vancouvers Island. 



Populus rotundifolia Newb. 



PL XXIX, figs. 1-4. 



Proc. II. S. Nat. Mus., Vol. V (March 21, 1883), p. 506; Ills. Cret. and Tert. PL 

 (1878), PL XIV, figs. 1-i, under P. cuneata. 



"Leaves of small size, rarely more than an inch in diameter, approxi- 

 mately circular in outline, either quite round or transversely or longitudi- 

 nally elliptical; slightly wedge-shaped at the base, and decurrent on the 

 long petiole; basal margin entire; upper half of leaf coarsely crenate, 

 dentate, and usually short pointed at the summit; nervation flabellate, con- 

 sisting of a median and two principal lateral nerves, which give off numer- 

 ous branches " 



