186 UNITED STATES GEOLOGICAL SURVEY— TERTIARY FLORA. 



merely roiinrlcd or pointed; fig. 4 of pi xxvi has the same form, and the 

 borders are only slightly undulate, while in fig. 5 of the same plate the borders 

 are perfectly entire. Hence, with these distinct modifications of characters 

 exposed to view, it would not be advisable to consider these leaves under 

 diiferent specific names, as I did formerly, before I had opportunity to recog- 

 nize the variations upon a large number of specimens. The size of the leaves 

 is, like the length of the petiole, as variable as in the other congeners. 



Habitat. — Golden, Colorado, in connection with P. Haydoiu; the spe- 

 cimen of pi. xxvii, fig. 3, is from the same locality, by Rev. A. Lakes; the 

 specimen of pi. Ixxvi, fig. 4, is from Black Buttes, Wyoming. 



Platanus I'liomboidea, Lesqx. 



PlateXXVI, Fig.s. 6,7. 

 Platanus rhomhoidia, Lesqx., Annual Report, 1873, p. 400. 



Leaves membranaceous or subcoriaceous, enlarged upward from a narrowed cuneiform base, 

 obscurely lobed above the middle, entire toward the base, deeply sharply dentate in the upper part ; 

 lateral nerves in an acute angle of divergence, parallel. 



The substance of these leaves is of the same consistence as in the former 

 species, either membranaceous or subcoriaceous; the shape is rhomboidal in 

 outline, largest at the middle, hence narrowed and entire to the base, broadly 

 lanceolate or subtruncate to the point, and there deeply dentate; the lateral 

 teeth entered by the lateral nerves being a little longer or passing to short 

 acute lobes. From the two only specimens in my possession, the leaves 

 of this species appear comparatively small, from seven to twelve centimeters 

 long and from five to nine broad. The nervation is Platanoidal, but the wedge- 

 shaped base of the leaves does not agree in character with that of Platanus 

 leaves, at least in a general point of comparison; for, as I have remarked 

 already, P. occidentalis has in some peculiar habitat all its leaves narrowed 

 to t.he petiole, but dentate to the base, aind even a variety of P. orientalis, 

 described as P. CKwm^ff, Willd., has them ciineate, and often entire downward, 

 in the same manner as our fossil species. The fossil leaves, however, are of 

 a more coriaceous substance. 



Habitat. — Golden, Colorado (Cajjf. E. Berthoud, Rev. A. Lakes). 



BALSAMIFLU^. 



LiaUIDAMBAR, Linn. 



The genus is represented in tlie flora of our ejioch by five species. One 

 of them, Liquidambar styracijiuum, Linn., the North American Sweet Gum, 



