238 THE FLORA OF THE DAKOTA GROUP. 



arctica, as its first and most generally distributed species, P. arclica Heer, is 

 represented in all the stages of the Tertiary, even in the small groups of" 

 plants of the auriferous gravel deposits of California, by numerous leaves 

 of P. ZdddacJti, its close relative. Of the second type or section the Laramie 

 Group has only three species. From the Green River Gronp six species 

 are recorded, belonging, with one exception, to the first section, and most 

 of them already present in the Laramie; and from the ten species descnbed 

 as Miocene, of which seven are from Alaska and the Bad Lands, six are also 

 referable to the first section. This section, which corresponds to that of the 

 coriaceous poplars, has no representatives in the present North American 

 flora. 



The first leaf of the Dakota Group referred to Platanus, I', py'tniccva, 

 is described and figured in Lesq., Cret. Fl., p. 60, PI. VII, Fig. 2. Its 

 character, form, and nervation are distinct, and their affinity to those of 

 P. accroides Gopp., of the ]\Iiocene, and P. occidenfalis, of the present North 

 American flora, is easily recognized. Prof Geinitz found in the general 

 aspect of that leaf a likeness to Credneria leaves, but Saporta has admitted 

 it in the Monde des Plantes, p. 202, Fig. 2, as the true, primitive type of Plat- 

 anus. Later, as is seen in the descriptive part of this volume, numerous 

 leaves of the same type, some of them very large, still more closely allied 

 by their uonnal characters and their varieties to those of 1'. occiderdfdis, have 

 been discovered, together with a flowering- raceme, and thus the presence of 

 this genus in the Dakota Group is fully confirmed. Besides the first-named 

 species, eight others are described from specimens of the Dakota Group, 

 two of which have been recognized in the schists of Atane in Greenland 

 and in the Milk liiver series of Canada, and two in the Upper Ch-etaceons of 

 Patoot. In the ITpper Cretaceous plants of Wyoming and Vancouver Island 

 no remains referable to Platanus have as yet been observed. But they 

 have been most abundantly found in the Laramie Group, where the form 

 of the leaves is somewhat modified in /'. Bai/noldsii Newb., P. Haydenii 

 Newb., P. nohilis Newb., P. rhoiuhoidea Lesq., and still more in /'. has'dolxdd 

 Ward, the heaves of which are adorned by basilar appendages somewhat 

 like stipules, as already remarked. 



In the Laramie Group also, leaves oi P. Guillclmcc Gcipp. have l)een 

 observed, and these are extremely frequent in the Miocene of Eiu-ope and 

 North America, together with those of P. ucerokhs. P. appendicidata and P. 

 dissecta, whicli is perhaps a variety of it, are so closely allied in character 

 to those of the living P. occklentalis, the North American Buttonwood, that 



