182 THE POTOMAC OR YOUNGER MESOZOIC FLORA. 



Potomac strata, and these alone give to tliis group of plants the considera- 

 ble importance that they possess in this flora. 



DiooNiTES BucHiANUS Schimper. 



PterophijUim Buchianum, Ettingshausen, Beitriigo z. Fl. der Wealdenperiode, p. 21, PI. T, Fig. 1. 

 Picrophjillum Saioniciim, Reich., Ettingshausen, Kreideflora von Niederschcona, PI. I, Figs. 11, 12. 

 Dioonites Saxonicns, Schimper, Traits de Pal^out., vol. 2, p. 211. 



Plate LXVIII, Fig. 1 ; Plate LXTX, Figs. 1, .3; Plate LXX, Figs. 2, 3; Plate LXXI, Fig. 1; Plate 

 LXXII, Figs. 1, 2; Plate LXXIII, Figs. 1-3; Plate LXXIV, Figs. 1-3. 



Leaves very large, attaining probably the length of a meter and over; 

 maximum width, 30"™ and over; rachis stout, showing a keel on the under 

 side ; epidermis over the rachis and leaflets thick and durable ; leaves thick 

 and leathery; leaflets varying much in dimensions, distance, shape, and 

 termination ; leaflets linear-acute, sometimes closely placed, sometimes 

 remote, those in the middle part of the leaf the most commonly found, 

 these going off" at an angle of 45°, those of the upper part more and more 

 oblique, until at the summit they occur in the prolongation of the mid- 

 rib, and the leaf is terminated by a leaflet, the terminal leaflets much 

 shorter and narrower than those lower down ; length varying, attaining in 

 some cases 2-'S™'; the leaflets slightly narrowed to the base and attached by 

 the whole width of the base, obliquely set on and decurrent ; epidermis 

 sometimes showing a granulation or a line of dots between the nerves; 

 nerves fine, very closely placed, forking at the base, parallel, and terminat- 

 ing without convergence in the summits of the leaflets, some of the outer 

 ones ending in the margins a little below the summit. 



Localities : All points on James River that yield plants, except Deep 

 Bottom ; especially abundant at entrance to Trent's Reach, in banks of 

 Dutch Gap Canal, and at fishing-hut above the canal ; very abundant at 

 Kankey's ; found also at all plant localities north of Kankey's to Fort 

 Washington, but not abundant beyond Telegraph Station. 



This splendid plant is one of the most widely ditfused and character- 

 istic fossils of the Potomac flora. At the entrance to Trent's Reach, in the 

 thin plant-bearing layer near the top of the bluff, the imprints are in places 

 very numerous, and much of the plant-substance is still retained, the relics 

 being matted together. Here it is found in company with Baieropsis 



