DESCRIPTION OF TUE SPECIES. 131 



This is one of tlie most widely diffused of tlie Potomac ferns. In 

 that respect it differs from most of the ferns of this formation, for they are 

 usually much isolated in occurrence. It does not seem to be nearly allied 

 to any known fossil. 



TlIYRSOPTERIS ANGU.STIFOLIA, sp. nOV. 



Pliite XLIV, FiK. 1; Pl.ate XLV, 1m^'. 3; Plato XLVIII, Fig. 2; Plate .XLIX, Figs. 3, 4; Plato LV, 

 Fig. 2; Plate LVIII, Fig. 8. 



Frond tripinnate, arl)orescent ; pinnules and lol)es narrowly oblong- to 

 acute; pinuiR and i)iiinnlL'.s usually much crowded; ultimate pinn.T and 

 pinnules alternate, diminisliing- in passing towards the ends of the com- 

 pound pinna^ into pinnules and lobes ; pinnules and lobes narrow, obliquely 

 cut, in shape narrowly oljlong to linear, lower puinules separate to base, 

 and furnished with narrowly elliptical acute lobes and acute teeth, passing 

 in ascending into more and more fully united narrowly elliptical teeth ; 

 nerves in each lobe of the upper pinnules forked, with the upper branch 

 forking again or single in some cases. In the lower pinnules the lobes have 

 a midrib with alternate simple branches going off on each side ; midrib and 

 lateral nerves of the pinnules all slender. 



Localities : Entrance to Trent's Reach ; fishing-hut above Dutch Gap 

 Canal ; 72d mile-post, near Brooke ; hill-side near Potomac Run ; not 

 common anywhere. 



This is a widely diffused fern. It is distinguished by the narrowness 

 of its lobes and pinnules and the absence of a wing on the rachises. It 

 belongs to the SpJtciiopteris Gtrppcrii type of Tlii/rsopfcris. Some of the 

 specimens sent from Professor Uhler's collection, gotten at Baltimore, to 

 New Orleans, and thus lost, were similar to this plant, and hence it 

 probably occurs at Baltimore. 



TlIYRSOPTERIS MICROPHYLLA, Sp. UOV. 

 Plato XLV, Figs. 1, 2, 4, 5. 



Frond tripinnate, large, arborescent; principal rachis strong; penult- 

 imate pinna? alternate, with strong rigid rachises comparatively short, ter- 

 minated abruptly by an ultimate pinna similar to those lower down on the 



