DESCRIPTION OF THE Sl'HCIliS. 133 



in the upper part of the conipouiKl piim;v. The nerves are tine but dis- 

 tinct, closely plai-ed, deeply forked, flabellately diverging in each lobe and 

 tooth, consisting of a slender midnerve, which sends off very oblicpiely 

 deeply forked or simple branches. 



Localities: Fredericksburg; road-side near Potomac Run; near Tel- 

 egraph Station; fishing-hut above Dutch Gap Canal ; rare everywhere. 



This fine plant l)elongs to the Spheiinptcris luiiijifolia type of Wealden 

 ferns. Its facies is one highly characteristic of the Potomac ferns, includ- 

 ing more forms than anv other. It is not clo.sely allied to any descriljed 

 fossil known to me. 



Thvrsopteris klliptica, sp. nov. 



Plate XXIV. I'ig. :i; Plate XLVI, Fig. I ; Plate L, Figs. G, il; Plate LI, Figs. 4, (i, 7 ; Plato LIV, Fig. 

 0: Plate LV, Fig. 4; Plate LVI, Figs. 6, 7; Plato LVII, Fig. G; Plato LVIII, Fig. 2. 



Frond quadripinnate, large, spreading, and arborescent ; rachises 

 strongly winged, keeled on the under side ; principal rachis very stout, and 

 often more or less flexuous; leaf-subtance of the pinnules thick; arrange- 

 ment of the ultimate pinna? A'arious. The plant shows a tendency to a pal- 

 mate mode of subdivision of the principal rachis (see PI. LVI, Fig. G); 

 compound pinna.' abruptly terminated by penultimate pinnje like those 

 down lower (see PI. LI, Fig. G); ultimate pinna' crowded, quite short; 

 lower pinnules of the ultimate pinn;B, in the lower part of the frond cut 

 more or less deeply and obli([Uely into narrowly oblong to elliptical 

 obtuse lobes or rounded teeth, separate to the wing of the rachis, obliquely 

 placed, much narrowed at the base, elliptical or ovate in shape ; pinnules 

 in ascending towards the sunnnit of the frond and ends of the compound 

 pinn;v pass into entire ellii)tical pinnules, and these, united more and more, 

 pass into lobes and teeth ; midnerve of the lobed piiuniles splitting at the 

 summit and sending off down lower alternately into the lobes branches 

 which fork once or twice ; branches in the upper pinnules either once 

 forked or simple. 



Localities: Fredericksburg, not uncommon ; red clay ball in banks 

 of Dutch Gap Canal ; rare. 



This j)lant is not very close to anv previouslv described fossil. 



