ANALYSIS OF THE DAKOTA GROT P FLORA. 249 



the Laramie Group. The hving flora of Europe lias no representation of 

 the Menisperniace*. 



The family StercuHace;c are inostlv represented in paleobotany by 

 species of Sterculia. The phints of this g-enus have leaves generally ])alMi- 

 ately divided from below the middle, the primary nervation (h*rived from 

 the top of the petiole at the basal l)orders, palniately tlii*ee to five parted, 

 and the secondaries numerous, either anastomosing in bows quite near the 

 borders or gradually effaced in passing into the areolation by repe.ited 

 anastomoses. These are the essential points which I have considered for 

 the attribution of leaves to this genus, especially as distinctive from those 

 of the leaves of Aralia, whose base is prolonged or deciu'ring along the 

 petiole and the primary nervation being palmately trifid and su})ra-l)asilar. 

 These characters may l)e considered of little practical value, but serve as a 

 diagnosis of the fossil leaves referred to Sterculia, and aff^ord the means of 

 comparing the march and distribution of these plants through the geological 

 ages from their origin in the Dakota Group, where they are- first recognized. 



I have referred to Sterculia seven species or forms of leaves of the 

 Dakota Group, some of tliem related to S. lahrusca Ung., a common and 

 variable species of the European Tertiarv. None have been recorded b\- 

 Heer from the schists of Atane, but one is recognized by DaAVSon in the 

 Peace and Pine River series of Canada. From the Upjjer Cretaceous, 

 Heer has described leaves of Sterculia rnriuhiUs, first descriljed by Saporta 

 in his Fl. Foss. de Sezanne, p. 400, PI. xii, Figs. 6, 7; and .S'. labnisca Ung., 

 a species commonly found in the Tertiary of Europe, is recognized in the 

 flora of Gelinden by Saporta and Marion. Finely preserved leaves of one 

 species, S. modesta Sap. (Fl. de Se'zanne, ]). 40, PI. xii, Fig. 2), have been 

 found at Golden, Colorado, (Laramie Group), and one species is described 

 from the Green River Group. Though sixteen species of Sterculia are 

 recorded from the Tertiarv of Europe, the genus is without representatives 

 in the present flora of Europe and of America. 



Tilia and Grewia, Ixith well characterized genera, have left abundant 

 remains of leaves in the Tertiary, and have representatives in the flora 

 of the present epoch. Grewiopsis and Apeibopsis, with less definite char- 

 acters, related as indicated by the names to Grewia and Apeiba, are 

 represented in paUv.oljotanv from the Cenomanian, but become extinct in 

 the recent stages of the Miocene. Apeibopsis ThomsoiidiKi Heer has been 

 described from the schists of Atane, and leaves scarcely difiering from those 

 of Atane have also l)een deseribed from the Dakota Group as A. rijclophjiJIa. 



