2 FOSSIL FLORA OF THE SIEEEA NEVADA. 



DICOTYLEDONES. 



AMENTACE^J. 



BETULA, L. 



Betula aequalis, sp. nov. 



PI. I. Figs. 2-4. 



Leaves elliptical-ovate, equally narrowed up to a sharp point and downward to a short 

 petiole ; borders equally dentate; secondary veins mostly simple, craspedodrome. 



The form of the leaves is the same in all the specimens, differing only 

 hy their size, from five to eight centimeters long, and from two to three 

 and a half centimeters broad. The secondary veins are mostly simple, 

 either slightly curving in passing up to the borders in an acute angle 

 of divergence of .30° or straight, entering the alternate teeth and some- 

 times the intermediate ones by short branches, as in Fig. 2. The lower 

 pair of lateral veins join the middle nerve a little above the base of the 

 leaves, which is generally bordered, at least on one side, by a thin mar- 

 ginal veinlet ; they are parallel, equidistant, opposite in the lower part 

 of the leaves, alternate in the upper part, generally separated by a thin 

 tertiary vein dissolved below the middle of the areas; the teeth, nearly 

 equal, are sharp, and slightly turned upwards. 



The relation of this species to the present Betula occidentalis, Hook., 

 commonly found along the streams of the Eocky Mountains, is very close 

 indeed. The nervation is the same ; the nearly equal teeth are, in some 

 leaves at least, of the same form and size ; the difference is only in the 

 shape of the leaves, which in the fossil species are longer, wedge-form 

 to the base, and also proportionally narrow. A fine representation of 

 this Betula is given in Watson's 4i Botany of the Fortieth Parallel," PI. 

 XXXV. Among the fossil species, ours is comparable to B. Brongnarti, 

 Ett. Fos. EL v. Bilin. I., p. 46, PI. XIV. Figs. 9-13, which is common in 

 the Miocene of Europe, and has been described also by Heer, Gaudin, 

 Saporta, and other palaeontologists. The affinity, however, is more marked 

 with the living American B. occidentalis than with any fossil forms known 

 as yet of this genus. 



Habitat. — Chalk Bluffs, Nevada County, California. Voy's Collection. 



