170 THE POTOMAC OR TOUNGER MESOZOIO FLORA. 



into segments of varying width, that are rectangular, irregularly quadrilat- 

 eral, or subrhombic in shape, and have often the posterior or outer mar- 

 gins obliquely rounded off; nerves very fine and placed very closely 

 together, so that two or three occur in the space of 1"", going off nearly at 

 right angles, curving very slightly forward, parallel. 



Locality : Fredericksburg ; not uncommon. 



This splendid plant has yielded a number of specimens, but all of 

 them, no doubt owing to the great size and to the fragility of the leaf, 

 show only small portions of the plant. The base and tip of the leaf were 

 in no case found, although carefully sought for. The specimen men- 

 tioned as 25"" long, with no sensible diminution in width, belonged to this 

 plant. One specimen showing only half the lamina of the leaf was 9™ 

 wide (see PI. XXXV, Fig. 2). This indicates a leaf 20™ wide. The tip 

 seen in Professor Uhlei''s collection seems to have belonged to this species. 

 This plant has the same kind of vaguely defined midnerve that was 

 described in Contributions to the Knowledge of the Older Mesozoic Flora of 

 Virginia, Mon. U. S. Geol. Survey, vol. 6, as belonging to Macrotceniopteris 

 magnifolia Rogers, of the Older Mesozoic or Rhaetic flora of Virginia. It 

 is due to the dense epidermis and leaf-substance at the junction of the lam- 

 ina of the leaf and the midnerve, which hides the insertion of the nerves 

 and widens the apparent midnerve. 



The nerves, although exceedingly slender and closely placed, are 

 sharply defined and have only one woody bundle, differing in this point 

 from those of the Rhaetic fern. They are usually one-half millimeter 

 apart, although sometimes only one-third of this. Fragments of the petiole 

 were very rarely seen. 



This plant may be compared with Nilssonia Johnstrnpi, Heer^ It is 

 very much like PterophjUum princeps Oldham and Morris,^ and also 

 strongly resembles Pterophyllmn Bramisii Schenk. Both of these are 

 Rhaitic plants, and both are placed by Schimper in his subgenus Platyp- 

 ierightm. Nilssonia JoJmstrupi seems to be a Platypterigkim surviving into 

 the Middle Cretaceous. 



' Flor. Foss. Arc, vol. 6, Part II, PI. VI, Figs. l-i3. 



2 Pal. Indica, Foss. Flor. Eajmahal, .Series II, vol. 1, PI. XII., Fig. 1. 



