DESCRIPTION OF SPECIES. 4g 



These leaves are generally small, being 2.5"'° to 6™ long, 1.5"" to 3*"° 

 broad at the middle, with a slender, long petiole which is generall}- broken. 

 The secondaries, at an angle of divergence of 45° variable in distance, more 

 or less ramose, are often separated by thinner, shorter, parallel tertiaries 

 and crossed by nervilles at right angles forming large meshes. 



By their torm and size they are closely similar to the small leaves of 

 P. mutahUls Ileer, a common and very variable species of the European 

 Miocene; they are, however, generally narrower, longer aeumii.ate and 

 always quite entire. They have been abundantly found mixed with those 

 of Diospyros roUmd'tfolia (Figs. 8-11 of the same plate) with which they have 

 a degree of resemblance, differing, however, always by the thinner texture 

 and the pointed or acuminate apex. 



Habitat: Ellsworth County, Kansas, in nodules. Nos. 411, 41 G, 471, 

 473, 480, 481, of the museum of the University of Kansas. Collected b}- 

 E. P. West. 



POPULUS HYPEKBOREA HeCr. 



PI. Ill, Figs. 9-11; PI. VIII, Fig. I; PI. XLVII, Fig. 5. 



neer, Fl. Foss. Arct., vol. 3, pt. 2, p. 106, PI. xxix, Figs. 0-9; PI. xxvii. Fig. 8d; PI. 

 XXX, Fig. 2b; vol. 6, Abtb. 2, p. 64, PI. xvii. Figs. 6, 7; PI. XXI, Fig. la. 



Leaves coriaceous, ovate or broadly oval, entire, obtuse, rounded at 

 base to a long petiole or slightly curved downward in reaching it; median 

 nerve strong; secondaries distant and ramose, camptodrome. 



All the leaves seen from this species from the Dakota Group are about 

 of the same size, that is 4"™ to 7"'" long, 5"™ to G""" bx'oad at the middle, with 

 a strong petiole 6"'" long. It is the same with the leaves figured by Heer, 

 except one,^ which does not seem to be referable to the species. They are 

 also identical in the other characters except that the leaves from Green- 

 land have the basilar border rounded to the petiole, as in PI. Ill, Fig. 11, and 

 PI. VIII, Fig. 1, not at all narrowing at base, as in Figs, i) and lU of PI. III. 

 The difference is, however, of no specific value. The nervation is more 

 distinctly marked in the leaves from Kansas, which are also better preserved. 



The lower secondaries are supra-basilar, l)ut have generally under them 

 quite near the base a thin pair of nervilles which follow close to the borders, 

 anastomosing with them; the u})})er ones are variable in distance, diverging 

 30°-40° from the midrib, little curved in traversing the blade, arched along 

 the borders which they follow, anastomosing in simple, large areoles. The 



'Loc. cit., PI. XXIX, Fig. 7. 



