144 THE POTOMAC OE YOUNGER MESOZOIC FLORA. 



posed in the lower lobes of a flabellately diverging- nerve-bundle, the 

 branches of which are forked or simple ; in the upper ones composed of 

 forking- nerves. 



Localities .- Ilill-side near Potomac Run ; near Telegraph Station ; 

 quite rare. 



Tliis seems to be a well-marked distinct species with a Sphenopteris 

 facies. 



Thyrsopteris rhombiloba, sp. nov. 



Plate LIX, Figs. C, T ; Plato LX, Fig. 8. 



Frond tripinnate, arborescent ; principal rachis stout ; ultimate ])inna^ 

 alternate, linear lanceolate in outline, terminating- in an acute lobed seg- 

 ment ; piniuiles closely placed, alternate, oblong or subrhombic, acute, 

 passing above into united lobes, cut more or less deeply into subrhombic 

 lobes, much narrowed at base, decurrent to form a wing on the penultimate 

 rachis ; nerves of the pinnules composed of a inidnerve which splits up at 

 the top and sends off pinnately into the lower lobes nerve-bundles which 

 diverge flabellately in the lobes, the branches being simple, or forked in 

 the lower lobes ; in the upper lobes the lateral nerves fork once or twice. 



Locality : Hill-side near Potomac Run ; not uncommon. 



The penultimate pinnae of this plant in the upper parts of the com- 

 pound pinnoi are reduced to pinnules, as is shown in PI. LX, Fig. 8, and 

 in the lower portions of the frond, as in PI. LIX, Fig. 6, they seem to pass 

 into ultimate pinnae. These do not have the rachis to which they are 

 attached winged. The plant seems to be a distinct new species. 



Thyrsopteris retusa, sp. nov. 



Plate LIX, Fig. 10. 



Frond tripinnate; principal rachis stout; pinnre alternate; ultimate 

 pinnae short, lanceolate in shape, rachis winged, terminating in a lobed 

 segment formed of united and reduced pinnules; pinnules towards the ends 

 of the ultimate pinnae passing into lobes and teeth ; those of the lower por- 

 tion of the ultimate pinnae much narrowed at base, united by decurrence 

 to form a wing, oblong-, terminating in three acute teeth, cut into retuse 



