292 THE POTOMAC OR YOUNGER MESOZOIC FLORA. 



CXLIV, Fig. 3, PI. CXLVII, Fig. 4. These unite with the main lateral 

 nerves or the larger branches from them, and form very large, irregularly- 

 shaped, lax meshes. Sometimes the principal net-work in the interspaces 

 of the main lateral nerves is formed by large branches from these; the 

 union of the principal lateral nerves, or of their main branches, makes a 

 row of well-defined arches near the margin of the leaf; the ultimate meshes 

 are quite uniform in size, mo.stly subrhombic in form, and not so sharply 

 defined as in most of the types with archaic forms of nervation from Fred- 

 ericksburg. 



Localities: Fredericksburg, quite common; Deep Bottom; fishing hut 

 above Dutch Gap Canal, rare. 



This singular plant must have had in some of its leaves a very great 

 size. This is indicated by such fragments of leaves as are shown in PI. 

 CXLIV, Fig. 3, and PI. CXLVII, Fig. 4, both of natural size. The midrib 

 especially is conspicuous for its great thickness. It, and especially its 

 extension as the petiole, seem to have been somewhat succulent. This was 

 much the largest species of leaf found at Fredericksburg. As these arcliaic- 

 looking leaves were the first ones found, and as I found it difficult to give 

 any characters which would distinguish them from ferns, I have given the 

 details of their nervation more fully than I would have done if the presence 

 of angiosperms had then been fully established in the Potomac flora. Up 

 to this time these strata have been held by most persons to be Triassic. 



The leaf, PI. CXL, Fig. 3, shows what might at first sight seem to be 

 a petiole, but it is reall)' a portion of the midrib from which the lamina of 

 the leaf has been stripped, and the basal portion of the lamina, still shown, 

 is doubled back and contorted. Plate CXLVIII, Figs. 1, 2, shows leaves 

 of the smallest size. 



The nervation of these leaves is a good deal like that of Dawson's 

 Ficus maxima, Cretaceous and Tertiary Floras of British Columbia. 



FiCOPHYLLUM TENUINERVE, Sp. nOV. 



Plate CXL, Fig. 3; Plato CXLI, Fig. 2; Plate CXLV, Figs. 1, 4; Plate CXLVII, Fig. 9; Plate 

 CXLIX, Figs. 1, 3, 5; Plate CLVI, Fig. 1. 



Leaves varying in size, sometimes attaining very considerable dimen- 

 sions, oval in outline, rapidly rounded off^ towards the base, where it is 



