136 THE POTOMAC OK YOUNGER MESOZOIC FLOEA. 



This, altlioug-li found only in one or two small fragments, seems to be 

 quite a distinct new species. It looks more like some of the Gleichenui' 

 from the Lower Cretaceous of Greenland than any other plant. 



Thyrsoptkris pinnatifida, sp. nov. 



Plate LI, Fig. 2; Plate LIV, Figs. 4, 5, 7; Plato LVII, Fig. 7. 



Frond tripinnatifid, arborescent; rachises slender; ultimate pinnse 

 alternate; primary pinnre towards the summit suddenly changing from 

 penultimate pinnae to ultimate ones (see PI. LVII, Fig. 7); ultimate pinnjc 

 short, closely placed, terminating in acute oval lobes, obliquely inserted, 

 alternate, changing in passing to the suuuuits of the principal pinna? and of 

 the penultimate ones into lobed pinnules and finally into entire pinnules, 

 nuich narrowed at base, and attached by the narrowly winged midnerve, 

 cut down nearly to the midnerve in their basal portions into narrowly 

 oblong or elliptic-acute pinnules ; towards their ends and higher on the 

 compound pinnaj the pinnules graduate into lobes and teeth ; pinnules a'nd 

 lobes minute ; nerves in the pinnules of the lower parts forked deeply, 

 with the upper branch forking again ; in the lobes higher simply forked. 



Locality: Fredericksburg. 



This elegant little plant is not very rare at Fredericksburg. It is 

 noteworthy for the very regular and elegant shape of the pinnules and 

 lobes and for their minute size. 



Thyrsopteris heteromorpha, .sp. nov. 



Plate LII, Fig. 1. 



Frond apparently palmately branching, with the primary pinna; radi- 

 ating from the top of the common stipe ; ultimate pinnse of the central 

 compound pinnae passing abruptly in ascending into obtusely lobed pinnules, 

 and at the top changing into entire elliptical pinnules ; ultimate pinnse 

 closely crowded, short, and obliquely inserted, passing in ascending into 

 lobed and finally into entire pinnules, those of the upper side of the penult- 

 imate pinuiB larger and more deeply cut than those of the lower side, those 

 towards the base of the penultimate pinnae cut into elliptical subacute 

 pinnules and lobes, which are narrowed at base and obliquely placed, the 

 pinnules of the upper side being sometimes crenately toothed; leaf-sub- 



