DESCRIPTIONS OF SPECIES. 83 



the general aspect of these leaves, there can be little question that the)- are 

 specifically distinct. 



Formation and locality: Tertiary (Green River group). Green River, 

 Wyoming. 



Planera variabilis Newb. 



PL LXVI, fig. 5-7. 



Proc. IT. S. Nat. Mus., Vol. V (March 21, 1883), p. 508. 



"Leaves lanceolate, to broad ovate; usually unsymmetrical, jjetioled; 

 summit acute, sometimes long-pointed; base rounded or wedge-shaped; 

 margins coarsely crenulate-dentate or sen-ate, with remote, appressed 

 teeth; midrib straight, strong; lateral nerves delicate, frequently alter- 

 nating stronger and finer, gently arched upward, terminating in the teeth 

 of the border; the finer intermediate ones sometimes fading out before 

 reaching the margin." 



Collected by Dr. C. A. White. 



Some of the various forms of leaves ascribed to Planera Ungeri fairly 

 represent those before us, and their generic resemblance is apparent; but 

 in our plant the leaf is more pointed, the serratures are coarser, generally 

 more obtuse, and, when acute, more appressed. 



Planera longifolia Lesq., has larger, more symmetrical, and less acute 

 leaves, with coarser triangular teeth. (See PI. LVIII, fig. 3.) 



From the other species described in this volume this may be distin- 

 guished by its greater size, more ovate form, coarser serrations, and 

 relatively smaller crenations. Planera emarginata Heer (Fl. Tert. Helv., 

 Vol. II, p. 61, PI. LXXIX, fig. 24) has much more acute teeth and more 

 bristling aspect- 

 Several figures have been given of this species, in order to show the 

 diversity of form it assumes, and it could be easily imagined that they 

 were specifically different; but coming as they do from one locality, and in 

 the large collections made from this, we have an unbroken series, all per- 

 vaded by a similarity of aspect, we must conclude that they are all from 

 one kind of tree. Possibly future collections will prove that the narrower, 

 more rigid form, with the deeply cut and acute serrations, and parallel, 

 nearly straight lateral veins, shown in fig. 7, belongs to a different species; 

 but in the very large number of Planera leaves before me it is impossible 



