with Descriptions of X, w Species of Fossil Pla 



from the base of the leaf; medial nerve straight, Birapl< - ip- 



porting very small nerves), except near the summit, where two or 

 three larger branches rise from it; lateral nerves, two pain on each 

 side, springing from a common point of origin ; loner pair arched 

 upward, nearly parallel with the margin of the leaf to which they 

 send off one or more simple branches; Becond pair <>f laterals 

 diverging from these at an angle of 30°, arohing upward, and run- 

 ning parallel with the midrib, terminating in the margin near the 

 summit, each giving off about three exterior branches, whiofa QUITO 

 upward, and terminate in the dentations of the border. 



This species by its general form and nervation, approach 

 closely to P. Smilacifolia, but the base is rounded (sometimes 

 slightly wedge-shaped), never distinctly cordate ; the Buperior 

 lateral nerves are not quite so much drawn together toward the 

 summit, and the margins are differently and much more 

 coarsely dentate. 



Alarge number of specimens of this species presenl an! 



and distinctive characters. They exhibit considerable varia- 

 tion in size, being from 1 to 3 inches in length, but in form, 

 nervation, and marginal dentation, they are alike. 



These specimens are derived from different Localities, and 

 without doubt represent a distinct Bpeciee which was Bpn 

 over the Tertiary Continent. 



By the character of the impressions left on the Btone,aa well 

 as by the coarse and unequal dentation of the margins, we 

 may infer an affinity between this and the downy-leafed pop- 

 lars of the present epoch, such as P.aJha of Europe, etc., while 

 in the smooth surface and finely denticulate or entire marg 

 of P. Smilacifolia, we have evidence of reserablfl I' 



tremuloidcs. 



There is no fossil species for which thU can •• • "• 



Some of the forms of P. crenata, Ungei I Sotrka, 



S. 1GT, Taf. xxxvi. figs. 2 6), resemble lh< I they 



are not so distinctly radiat. ed. Unger rep 



teeth of the margin ae more acute, and more lik< I I P. 



tremida, with which he compares hie foaeil -; 



