DESCRIPTION OF THE SPECIES. 171 



Platyptkrigium Rogersianum, s]). nov. 



Plato XXXI, Fig. 2; Plate XXXIII, Fig. 2 : Plato XXXIV, Fig. 2. 



Leaf large, rivaling- the dimensions of P. dcnsinerve; leaf-snbstance 

 thicker and more coriaceou.s than that of P. (lensincrre. Tt is comparatively 

 strong- and coriaceous; midrib well defined, rounded, and prominent, 

 rigid, and without apparent dense epidermis ; nerves comparatively strong, 

 towards the base of the leaf going off more obliquely, higher and towards • 

 the middle of the leaf going off at a right angle, simple, straight, and par- 

 allel, more remote than those of P. dcnsinerve, being 1 """ apart. 



Locality : Fredericksburg ; rare. 



This fine plant is much rarer than P. densincrve. It is a more robust 

 species than the latter. It is not so prone to segmentation as that species, 

 possibly from its denser and stronger leaf-substance. One specimen was seen 

 11"™ wide, and in a length of I'i"'" showed no division into segments. I 

 have named the plant in honor of Prof William B. Rogers, who first studied 

 the geology of the Potomac formation and called attention to its plants. 



ZAMITES, Brong., emend. 



Leaves small or of medium size, in growing old becoming detached ; 

 leaflets attached to the upper side of the rachis by a callosity, somewhat 

 contracted or rounded at base, almost cordate there, linear or ovate- 

 lanceolate, acute or obtuse, margins entire, of firm consistency ; nerves 

 simple or forked, the middle ones parallel, diverging only towards the 

 summit, the lateral ones ending in the margin. 



This description, which is essentially that given by Schimper,' applies 

 to some detached leaflets found in the Potomac flora. They are alwa3-s 

 among the rarest of fossils in this flora, appearing only in sparingl)^ dis- 

 persed fragments. They form a very inconsiderable element in the Poto- 

 mac flora, being found mostly at Fredericksburg. 



Zamites tenuinervis, sp. nov. 



Plate LXVII, Fig. 1; Plato LXIX, Fig. 2; Plato LXX, Fig. 1; Plato LXXV, Fig. 3; Plato LXXVI, 

 Fis. 7; Plato LXXVIII, Fig. 6; Plate LXXXIV, Fig. 7. 



Leaflets very long, attaining the length of 20.5'"' and a width of 

 24"", at base abruptly subcordate, in shape ensiform, sometimes curved, 



^ttel'S HaQdbnch der Pahoont., vol. 2, Lief. 2, p. 218. 



