250 THE FLORA OF THE DAKOTA GROUP. 



At rt liigher stage of the Cretaceous, in Montana, another species of Apeibopsis 

 is also found. The genus Grewiopsis is less positively recognized. Numerous 

 leaves of tlie Dakota Group have been referred to this genus under the spe- 

 cific name of G. Hai/dpiiii. By their nervation they have a degree of affinity 

 to those of Tiliii. A fruit also of Nordemkidldla Heer, a new genus whose 

 relation is apparentl y to the Tiliacese, is described from the same formation. 

 Taken altogether, these remains bear testimony to the origin or presence of 

 the Tlliaceaj in the Dakota Grou]). Of nine species to Grewiopsis recorded 

 in the H(ira of the Laramie Group, five are described by Prof. Ward and 

 four by myself. The genus Grewia is first recognized in the Laramie 

 Group by four species, and later in the Miocene of Oregon by one ; four 

 species of Grewia are also described by Heer in his Fl. Foss. Ai-ct, all from 

 the Tertiary of Cape Lyell, Spitzbergen. 



Leaves of Tilia have not been observed in the fossil flora of North 

 America before the Tertiary. T. aiitiqna Newb. (VUiHnnon fUinhles Wiird) 

 is from Fort Clark; another, T. popiilifolia Lesq., is from Florissant, in the 

 Green River Group. Tilia Malmgreni Heer, and T. alaskana Heer, are 

 reconled from the Arctic Miocene, or Eocene as it is now called. 



Ettingshausen tirst described in his Kreidefloi'a of Niederschoena, as 

 Acer antiquum, a leaf attributed to this genus, from its similarity f>f form to 

 those of A. decipiem Heer. This attribution was, however, generally con- 

 sidered dc^ubtful, and the origin of the genus referred to Tertiary age. A 

 number of leaves recently discovered in the Dakota Group of Kansas and 

 described under the name of Acerifrs innUifnrmis (PI. XXXIV, Figs. 1-9), 

 confirm, bv their characters, the determination of Ettingshausen and prove 

 the existence of representatives of this family in the Cenomanian. 



No remains of Acer have been found in the schists of Atane, but Heer 

 has recognized two species in the Senonian of Patoot, and in more recent 

 formations from the base of the Laramie Group fossil remains of plants of 

 this gemis have been found in abundance. In the Tertiary of Greenland 

 Heer hiis ten sijecies. Prof Ward has described two in his Laramie flora, 

 and I have found seven species in the different stages referred to the Lar- 

 amie, and two species in Upper Miocene strata of the auriferous gravel 

 deposits of California. More than sixty species of Acer and two species of 

 Negundo are described from different stages in the European Tertiary. 

 In the living flora fifty or more species are known, mo.stly inhaliiting 

 the northern luiuiisphere, and being equally distributed between Europe 

 and North AmHrica; seven species in Europe, five in the Atlantic States of 



