DESCRIPTIONS OF SPECIES. 53 



safer to consider it only an unusual form of fig. 1 and refer it provisionally 

 to the same species. Its geological value will be secured by the truthful 

 figure given of it. 



Formation and locality: Tertiary (Eocene?). Yellowstone River, Mon- 

 tana; Fort Union, Dakota; Carbon Station, Wyoming. 



Populus smilacifolia Newb. 



PL XXIX, fig. 5. 



Ann. X. Y. Lye. Nat. Hist,, Vol. IX (April, 1868), p. 66; Ills. Cret. and Tert. PI. 

 (1878), PL XIV, fig. 5. 



"Leaves ovate, pointed, slightly cordate at the base; margins finely 

 and obtusely crenulated; nervation radiate, delicate and sparse; medial 

 nerve straight, giving off only fine and scarcely perceptible lateral ■ nerves 

 below, and two or three longer branches near the summit; two pahs of 

 lateral nerves radiate with the medial nerve from the same point at the base 

 of the leaf; of these the lower two are small, nearly simple, and arched evenly 

 upward ; the other two, nearly as strong as the midrib, spring from the base 

 at an angle of about 25 degrees, and after diverging to the middle of the 

 leaf, curve upward toward the summit, near which they terminate in the 

 margins. These lateral nerves support four or five simple or once-forked 

 branches, each given off exteriorly, which curve upward, and terminate in 

 the lateral margins. The tertiary nerves are given off nearly at right 

 angles from the secondaries and form a delicate polygonal or quadrangular 

 network over the surface of the leaf." 



Collected by Dr. F. V. Hayden. 



The lower pair of lateral nerves should properly be considered as 

 branches of the larger ones, so that the leaf is more distinctly three-veined 

 than that of any living species of Populus. This character, with the 

 smooth surface and nearly entire margins, gives these leaves the general 

 aspect of those of Smilax and suggested the name given them. Their 

 nervation, however, is sufficiently distinct from that of Smilax, and is 

 clearly that of Populus, though in a somewhat exaggerated form. In 

 Smilax three or five nerves radiate from the base of the leaf and terminate 

 together at the summit, which those of the leaves of Populus never do. In 

 Smilax, too, the principal nerves give off no large branches, but all the 



