142 THE POTOMAC OR YOUNGER MESOZOIC FLORA. 



Thyrsopteris in^quipinnata, sp. nov. 



Plate LVII, Figs. 3, 8. 



Frond tripinnatifid ; rachises slender ; ultimate pinna> opposite or sub- 

 opposite, of unequal length on opposite sides of the penultimate rachis, 

 rather remote, graduating above through lobed and dentate into entire pin- 

 nules, the latter being at tlie summit of the compound rachis and becoming 

 more remote in the upper part ; pinnules opposite, elliptical, much narrowed 

 at the base, passing towards the summit of the ultimate and primary 

 pinnte into entire ones, the lower ones cut into shallow, elliptical, subacute 

 teeth ; nerves fine, in the piimules composed of a midnerve which in the 

 toothed lower pinnules sends off very obliquely and alternately flabellate 

 nerve-bundles with forking or simple branches, and splits up into branches 

 at its summit; in the entire })innules it gives off in like manner lateral 

 nerves that are forked or simple. 



Locality : Fishing-hut above Dutch Gap Canal ; rare. 



The marked inequality in the length of the ultimate pinnjc on opposite 

 sides of the principal rachis is the most noteworthy feature of this small 

 plant. It seems to be unique. 



TnYRSOPTERIS HETEROPHYLLA, Sp. nOV. 

 Plate LVIII, Fig. 3. 



Frond probably tripinnate; rachises slender; penultimate pinnre alter- 

 nate, short, closely placed, terminating in a three-lobed segment, with 

 broadly winged rachis ; pinnules remote, those on the upper side larger 

 and less obliquely placed than those on the lower side, much narrowed at 

 base, and decurrent to form a broad wing, cut more or less deeply into 

 ovate teeth, elliptical to subrhombic in shape; leaf-substance thick; nerves 

 distinct, pinnately departing from a slender midnerve, simple, one in each 

 tooth. 



Locality: Fredericksburg; very rare. 



Although only a small fragment was found, this plant seems to be a 

 distinct species. It is much like Thyrsopteris Maahiana^ Heer. 



' Compare Flor. Foes. Arc, vol. 4, Part II, Beitriige zur Jura Flor., etc., PI. I, Fig. 1". 



