with Desertions of X, w Species of Fossil /'/., 



hardly be doubted that we have here the progenitor of on< 

 more of the group of poplars with which I have compared it. 

 and which now grow in the region where these fossil plants 

 were collected. 



The different species of Pqpulus, among the Miocene plants 

 collected by Dr. Harden, are far more generally three-nerved 

 than are the living species which now inhabit this country. 

 In this respect they resemble more the foreign P. alba ; and it 

 may be said that the majority of Bpeciea described in this 

 memoir are more closely allied to the section Coriaoea than to 

 the Balsam Um. 



Formation and Locality. Lignite Tertiary beds. Banks of 

 Yellowstone River. (Dr. Hayden.) 



Popultis Acerifolia. (n. sp.) 



Leaves long-petioled, broad-ovate in outline, often somewhat tin 

 lobed, obtuse, slightly cordate at base, margins coarsely and une- 

 qually crenate; nervation radiate, strong; medial nerve Btraight, giv- 

 ingoffonepairof lateral nerves near the cent iv of the leaf, and above 

 these about three smaller ones on each side. From the base of the 

 midrib spring two pairs of lateral nerves on each Bide. Of these 

 the lower and smaller pair diverge at an angle of 60* 7"- with the 

 midrib, are nearly straight, give off numerous short branches i D 

 the lower side, and terminate in the lateral margin below th«' mid- 

 dle. The second and larger pair of laterals diverge from the mid- 

 rib at an angle of about 35° to 45°, are straight or slightl) curv< 1 

 upward, terminating in the margins above the middle, or in the 



lobes, when lobes are developed; from these spring tin. r four 



branches on the outside, which, simple or branching, terminate in 

 scallops of the border. The tertiary nervation, bIiowu \> 

 tinctly in some of the specimens, form- a network Bitnilar t" thai 

 the leaves of living species of Populue, of which the ibil 



considerable diversity of form and size, being polygonal wit! 

 roundish outline, or quadrangular. 



The genera] aspect of these leav< - i- much i 

 of the living maples, but they are less distinctly trilo 

 crenation of the margin is coarse, irr< gular, and obi 

 rounded, as is usually the case with the I- 



APRIL, 1868. 5 • "'*' . '• 



