500 MESOZOIC FLORAS OF UNITED STATES. 



found, the rest being generally small fragments of leaves. This seems 

 to be correctly separated from Populus potomacensis b}'^ Professor 

 Ward. It is rarer than the latter, only 9 specimens having been 

 found. It is confined to the Mount Vernon locality. PL CX, Fig. 5, 

 gives a proportionally broader form than that figured by Professor 

 Ward. This specimen occurs in counterparts, and was collected on- 

 May 14, 1893, along with two others. Of the 5 specimens obtained on 

 November 6, 1892, this one is that figured by Professor Ward. 



Populus potomacensis Ward ?. 



This beautiful little leaf was first found by Professor Ward, and it 

 was fully described by him." It is very abundant in the Mount Vernon 

 strata, and in fact seems to be practically confined to them, so that it 

 may be regarded as their most characteristic fossil. A number of leaves 

 may be found nearl^^ or quite entire. This is surprising when we 

 consider their delicate texture, but the fact may be explained by their 

 very small size. 



All but three of the specimens were found at the Mount Vernon 

 locahty, that represented by fig. 1 of Professor Ward's paper being one of 

 those coUected by him on his first visit, on October 16, 1892. His fig. 3 

 represents a specimen that occurs on the reverse of one of the counter- 

 parts of the type specimen of Antholithes Gaudium^-Rosce, collected on 

 November 6, 1892, and his fig. 2 represents one of the few specimens that 

 were taken on the occasion of my visit to the locality, under his guidance, 

 on July 25, 1893. It shows the maximum size. 



Genus POTAJMOGETOPHYLLUIM * Fontaine nov. gen. 



The true position of this genus can not be determined from the 

 material at hand, and the generic name is chosen only to indicate its 

 resemblance to Potamogeton in points that may not be essential. 



PoTAMOGETOPHYLLUM VERNONENSE Fontaine n. sp. 

 PI. CIX, Fig. 7. 

 A very rare leaf, resembling Potamogeton, occurs in the Mount 

 Vernon collections, one specimen only being found in counterparts. It 



"Op. cit., pp. 355, 356, pi. iv, figs. 1-3. ' 



6 As the second component {yHrwv) of the name Potamogeton is itself derived from yin, yfi, and 



its immediate derivative, yijryi, this shortened form, which drops the characteristic n, i* fully justified. — 



L. F. W. 



