174 UNITED STATES GEOLOGICAL SURVEY— TEKTIAEY FLORA. 



border base of the leaves. In our specimens, as seen in the figure, the dis- 

 tance is still greater than in that of the Fl. Tert. Helv. Prof. Heer remarks 

 also that he has had for examination a large numl)er of specimens of the 

 same species, but that in all, except one, which he has figured, the upper part 

 of the leaves is destro^'ed, as it is in ours. He mentions, as distinctive char- 

 acters, the acutely serrate borders of the leaves, and the middle nerve thicker 

 than the lateral ones, the same as seen upon our specimen. I believe, there- 

 fore, that the identification of this leaf with the European species is fully 

 authorized. Heer considers this species as allied to the living P. dilatata, Ait, 

 and P. nigra, Linn. 



Habitat. — Point of Eocks, Wyoming {Dr. F. V. Hayden). 



Populus luel anarioides, Lesqz. 



Plate LXII, Fig. 5. 



Populus melanarioidca, Lesqs., Annual Keport, 1874, p. 302. 



Leaves long-potioled, subcoriaccous, nearly round, eubtruncate nt base; borders entire, nndu- 

 late; nervation teruate from .above the base; secondary veins, two pairs, at a groat distance from 

 the primary ones, these much branched ontside, the others simple ; divisions passing to near the bor- 

 ders or entering them. 



By its subcoriaceous substance and the long petiole of the leaves, this 

 species is related to the section of the Trepidce (Trembling Poplars). As in 

 Pojju/us treinulafolia, Sap. (fit., 3, 2, p. 26, pi. iii, fig. 4), to which our species 

 is allied, the veins and their brandies pass through the areas to very near the 

 inflated borders, which tliey seem to reach, but along which they are really 

 curved. Our leaf differs from those of this last species merely by less distinctly 

 undulate borders, by the higher position of the primary lateral veins above 

 the base, and by the great distance of the secondary less numerous veins. 

 These two last characters are, however, of no moment in the specification 

 of Poplar leaves, as can be seen in the examination of a few specimens of 

 Populus alba. In fossil species, also, as in P. Mosdliensis, Sap. (Et., 3, 2, 

 p. 30, pi. ii, figs. 6-8), the three leaves which represent it have each a different 

 type of nervation. The relation of our leaf to that described by Saporta from 

 the Tertiary of Provence may be therefore more intimate than it appears 

 from the comparison of a single leaf It is also comparable to Populus helia- 

 dum, Ung., by its form, and to P. ?nelanaria, Heer, by its nervation. 



Habitat. — Point of Rocks, Wyoming (J-Fw. Cleburri). 



