DESCKIPTION OF THE SPECIES. 121 



Locality: Ilill-side near Potomac liuii; verv rare. 



This plant is not unliko the undeterminod plant PI. XXI, Fig. 12, and 

 may be the same. The fragments found are too small and rare to ])ci-mit 

 its true nature to be made out. It is a little like Ileer's plants, Adiuntitcs 

 Ni/nipharum, and Dicksonia (Asplenium) Johnstrujn. 



Thyrsopteris brevifolia, sp. nov. 



Plato XXIV, Figs. .'., 10. 



Frond Itipinnate or tripinnate; rachises slender; ultimate pinna- long, 

 going otT at a large angle and slightly curved upwards, linear, alternate; 

 pininiles all very short in proportion to their width, lower ones separate to 

 the base, upper ones united to form a narrow wing ; pinnules much nar- 

 rowed at base, cut obliquely more or less deeply into lobes or teeth accord- 

 ing to position on the frond ; lobes of the lower pinnules cuneiform or nar- 

 rowed at base, very obtuse, fan-shaped and emarginate; of the upper ones, 

 oblong or ovate, very obtuse, towards the ends of the pinnae reduced to 

 oblong or ovate blunt teeth or lobes; nerves in the lower lobes of the 

 lower pinnules flabellate, remote, forking once or twice in the ujjper lobes 

 of the lower pinnules, and in the upper pinnules single, all quite distinct. 



Locality: Red clay l)all in the banks of Dutch Gap Canal; rare. 



This well characterized and elegant little plant is near to Sphenopteris 

 dissoeialis Phillips. It reminds one also of Sp]u')ioptcris hi/mcitojiln/Uo'ules 

 Brongn. 



Thyrsopteris dentata, sp. nov. 



Plate XXIV, Figs. 4, 6, 7. '.) : Plate XXV, Figs. 1, 2. 



Frond bipinnate or tripinnate, arborescent?; leaf-substance thick; 

 rachises narrowly winged; compound pinnaj terminating in a lobed acute 

 segment ; ultimate pinna? or pinnules opposite or subopposite, reduced 

 towards the ends of the compound pinnir to dentate pinnules, and at the 

 summit to united lobes; united at base to forma narrow wing, those of 

 the lower j)art of the frond cut deeply into oblong or subquadrate spiny- 

 toothed lobes or [)innules ; those higiier up have obliquely cut lobes and 



