Maryland Geological Survey 465 



Description. — The type of this species was a small, thick, orbicular 

 leaf with obscure venation from Federal Hill which the describer com- 

 pared with a Lemna. The same author has identified this species in 

 more recent collections and it is from these that the present description 

 is drawn since the original type presents no distinctive characteristics. 



Leaves peltate, considerably smaller than those of the preceding 

 species, not over 7 cm. in maximum diameter, orbicular in outline, the 

 transverse somewhat greater than the longitudinal diameter. Margin 

 entire or obscurely undulate. As might be expected from the com- 

 parative size, the veins are finer and the leaf substance is thinner than 

 in N. virginiensis. Veins radiating from the eccentric point of attach- 

 ment of the petiole, about seven in number, thin and somewhat flexuous, 

 forking and forming transverse loops parallel with the margin. These 

 loops send off almost rectangular branches forming a secondary series 

 of loops parallel with the margin. Similarly a third and smaller series 

 may be present. Veins obsolete on the upper surface of the leaf but 

 prominent below. 



This species is not strikingly different from the preceding, its specific 

 characters possibly being due entirely to its smaller size, although the 

 attachment to the petiole is nearer the margin, the transverse diameter 

 is proportionately greater, and there is a more definitely marked midrib 

 than in N. virginiensis. 



Occurrence. — Patapsco Foemation. Federal Hill (Baltimore), 

 Maryland; Mt. Vernon, Aquia Creek, White House Bluff, Virginia. 



Collection. — U. S. National Museum. 



Family MENISPERMACEAE 



Genus MENISPERMITES Lesquereux 

 [U. S. Geol. Surv. Terr., vol. vi, 1874, p. 94] 



The genus Menispermites was erected by Lesquereux in 1874 for the 

 reception of four species of leaves from the Dakota sandstone of the 

 West, which he had previously referred to Donibeyopsis, Acer or Acerites, 

 and Populites. His diagnosis was as follows: 



