DESCRIPTION OF SPECIES— SALICINE^. 177 



Populiis Ricbardsoiii, Heer. 



Plate XXII, Figs. 10-12. 



Populua Bichardsoni, Heer, Fl. Fobs. Arct., i, p. 98, pi. iv, figs. 1-5; vi, figs. 7,8; xv, fig. 1 c; ii, p. 468, pi. 

 xliv, figs. 7-9; Iv, fig. 3 6; Spitzb. Mioc. Fl., p. 54, pi. x, figs. 8-12. — Lesqx., Annual Report, 

 1873, p. 411. 



Leaves broadly ovate or nearly ronntl, trnnc.ate or slightly emarginate at the base, deeply irregu- 

 larly crenate, palmately five-nerved ; primary lateral nerves about as thick as the midrib, the upper 

 ones at an acute angle of divergence, ascending to near the point, branching in right angle or in a 

 broad angle of divergence. 



As recognized from European specimens, the leaves of this species are 

 very variable in size, mostly broadly oval or round, even broader than long, with 

 their borders deeply cut in irregular round teeth, a character which is clearly 

 defined in figs. 11 and 12 of our plate. They are described as acuminate, and 

 appear to be so in two figures of the author; but, in others, they are evidently 

 obtuse, a character remarked upon the leaf of our fig. 12. There is a great 

 difference in the relative position of the primary lateral nerves, which gen- 

 erally come out from the top of (he petiole, as in fig. 10, but which in fig. 11 

 become distant, the internal ones being far above the base of the lamina and 

 of the lower ones. That this difTerence is unimportant for specification is 

 evidenced by the nervation of the leaf in fig. 12, whose basilar nervation is 

 intermediate between that of the two others. This species is, by its char- 

 acters and its habitat, closely allied to the former. It is one of the most 

 common of the Arctic Regions, but has not been found either in the Baltic 

 or the Alaska Miocene. 



Habitat. — Elko Station, Nevada (Prof. E. D. Cope). It is represented 

 in the collection by six specimens, being therefore abundant at the locality. 



§ IV. — Coriaceoi. 



Populiis mntabilis, var. f. o v a I i s , Heer. 



Plate XXIV, Figs. 3, 4. 



Populus mutabilis f. ovaliaf, Heer, Fl. Tert. Helv., ii, p. 22 ; i, pi. i, figs. 1,2; ii, figs. 2 a, 6; ii, pl. Ix, fig. 

 12 b; Ixi, figs. 1-3, 6, 9 ; Ixiii, fig. 4.— Lesqx., Annual Report, 1871, p. 292 ; 1872, pp. 401, 405 ; 

 1873, p. 307. 



Leaves coriaceous, long, petiolate, oval, pointed, narrowed or rounded to the petiole; borders 

 entire ; nervation three- or five-p.ilmate. 



The references to the descriptions in the reports apply to different 

 varieties of this species, some of which have not been figured, on account of 

 the deficiency of the specimens, or from their exposition upon large rocks 

 which could not be displaced or broken. These varieties are so numerous 



12 T F 



