DESCRIPTION OF SPECIES— ANAOxVKDIACE^. 291 



ions being very similar. Pterocarya meioly difTers, in the characters of its 

 leaflets, by more distant and irregular secondary nerves. But this character 

 does not, seem any more marked in this leaf than in some other fossil ones 

 described by authors as Carya, especially C. elcenoides, Heer. As this 

 fragment comes from tlie Upper Miocene of the Rocky Mountains, and as 

 Pterocarya is an Asiatic genus, and therefore representative of a flora to 

 which the North American has no analogy, it would be more advisable to 

 consider the fragment as that of a leaflet of Carya or of Juglans. 



Habitat. — Middle Park, Colorado; a single specimen {Dr. F. V. Hayden). 



ANACARDIACE^. 



RHUS, Linn. 



This genus has, in the present flora, a large number of species, especially 

 inhabiting the subtropical regions, mostly in Southern Africa and North and 

 South America. The flora of the United States has nine species, three of 

 which are limited to the Pacific coast. In the geological times, this genus 

 is represented in the Lower Miocene of Europe, the Armissan especially, 

 by nearly fifty species, a number of which are found higher, in the Upper 

 Miocene, but none as yet in the Pliocene. In the fossil flora of North 

 America, it appears in the Lower Lignitic Eocene in two species, is 

 present in the Evanston group, more abundant in the Upper Miocene, and 

 predominant indeed in the Pliocene of California, which has a number of 

 its representatives, especially of the types of R. Typhina and R. metopium, 

 two sections mostly, if not exclusively, American at our epoch 



Rlius Evansii, Lesqx. 

 Plate L, Fig. 4 ; Plate LVIII, Figs. 5-9. 

 Wma Evansii, Lesqx., Aonual Report, 1871, p. 29;!; 1872, p. 402. 



Leaves pinnately compoiiiul ; leaflets variable in size, ovate-lauceolate, acuminate, round or 

 Bubcordate to the petiole; borders deuticulalo ; nervation craspedodrome. 



These leaflets seem at first to represent two species, the one (fig. 5) 

 having, by its shape and size, an appearance different from that of the smaller. 

 But, in closely comparing them, the same characters are recognized in all; 

 the lower lateral nerves of fig. 7 are branched, like those of fig. 5 ; both have 

 short marginal veinlets under the basilar j)uir of" nerves, and, except for 

 fig. 6, the divisions of the borders are simple and identical ; this fig. 6, there- 



