180 UNITED STATES GEOLOGICAL SURVEY— TERTIARY FLORA. 



centimeters long. The surface is not rugose or crumpled, but rather 

 smootli. T!i(! borders arc perfectly entire, not even undulate, and the 

 consistence is coriaceous, somewhat less so than in the former species, 

 which it resembles by the shape of the leaves and by the nervation. The 

 primary nerves, however, are ranch thinner, the nervilles closer, strong, the 

 upper ones passing to secondary nerves, or altogether taking their places, as 

 in the fragment of the left side of fig. 9. In other leaves, however, the 

 distribution of the secondary veins is the same as in P. a?xtica,oi' which 

 this new species seems to be like a diminutive form. It has also a great 

 similarity to Paliurus columbi, Heer, whose leaves are -found both at Carbon 

 and Creston, mixed with those of this Fopulus, and undistinguishable when 

 the petiole is destroyed. This remarkaljle likeness is seen in comparing for 

 example fig. 10, whose petiole is shorter and thicker than in the other leaves, 

 with figs. 14 and 15 of our pi. 1. The identity of habitat and the similarity 

 of characters in these leaves has rendered their separation difficult, and for 

 some of them uncertain. 



The relation of the.se two last species to Populus has been controverted, 

 for the reason that no point of comparison is found at our time among living 

 species of Poplars. The shape and nervation of the leaves have some like- 

 ness to those of Cercis, these of P. decipiens resembling for example C. antiqua, 

 Sap. (fit, i, p. 134, pi. xiv, fig. 4 a). This attribution is, however, contradicted 

 by the long petiole of both the American Miocene species and by a marked 

 diflerence in the details of the nervation. 



Habitat. — Creston, Washakie group {Dr. F. V. Hayden) ; Carbon, Wy- 

 oming, shale above the main coal, as common there as P. arctica. 



Populus mouodon, Lesqz. 



Plate XXIV, Figs. 1,2. 



Populus monodon, Lesqx., Trans. Am. Phil. Soc, vol. xiii, p. 413, pi. xv, figs. 1,2 ; Aunual Report. 1871, 

 Supplement, p. 13 ; 1073, p. 375.— Schp., Pal. V^g6t., ii, p. 699. 



Leaves large, corioceous, entire or undulate, broadly ov.ite, I.anceol.ate or taper-pointed, rounded 

 to the base ; primary nerves b.asilar. 



The two first leaves of this species described from the Mississippi have 

 the borders undulate, one of them being marked by a single obtuse short tooth. 

 This difference, the only one remarked between them and those figured here, is 

 • of no specific value. These leaves are large, from eight to sixteen centimeters 

 long, and from six to twelve centimeters broad toward the base, those of the 

 Mississippi being still larger. The very thick midrib, the slender secondary 



