126 THE POTOMAC OR YOUNGER MESOZOIC ELORA. 



pinnae alternate or subopposite, short, and in the lower portion of the frond 

 spreading ; j)innules in the basal portion of the ultimate pinnae, in the 

 lower part of the frond, cut deeply and obliquely into subacute, elliptical, 

 or subrhombic lobes, passing in tlie upper part of the ultimate pinnte and 

 of the frond through round-lobed pinnules into entire elliptical and acute 

 ones, and finally into lobes of the same shape ; nerves in each lobe flab- 

 ellately diverging, composed of a midnerve which sends off alternately on 

 each side branches either forked or simple. 



Localities: Baltimore, collected by Professor Meek; Fredericksbui-g ; 

 fishing hut above Dutch Gap Canal ; one small fragment from Covington 

 street, Baltimore ; rare at most localities, but one of the most common 

 ferns in Meek's collection made at Baltimore. 



This is a Potomac Thyrsoptcrid of the Sphenopteris type. In some 

 features it is like certain Potomac plants described under other names. 

 In lolling it is somewhat like Thyrsoptens hrevipennis, but the facies is 

 quite different, the rachis is stouter, the lobes and pinna; are more acute, 

 elongate, and crowded. 



Thyrsopteris Meekiana, var. angustiloua, sp. nov. 



Plate XXXVIII, Figs. 5-7, 9; Plate XLIII, Fig. 8; Plate XLIV, Fij;. 3; Plate XLVII, Fig. 4; Plate 

 XLVIII, Fig. 1; Plato LIV, Figs. 2, 11 ; Plate LV, Fig. 1 ; Plate LVI, Figs. 1, H. 



Frond tripinnatifid, arborescent ? ; rachises comparatively slemler ; 

 pinna3 and pinnules subopposite to alternate ; pinnules of the lower jjarts 

 of the compound pinn;B cut deeply and very obliquely into narrowly ellip- 

 tical acute lobes or teeth ; pinnules of the upper 2:)ortions passing through 

 those with elliptical or ovate teeth into entire ones; nerves as in T. Meeki- 

 ana, but less spreading and not so copiously branched. 



Localities: Baltimore, common in the plants collected by Meek, 

 occurring on the same pieces of shale with T. Meekiana, and almost as 

 abundant as that species; fishing hut above Dutch Gap Canal; Fredericks- 

 burg; 72d mile-post, near Brooke. 



This plant has the same general character as T. Meekiana, but is 

 more slender than that and has the pinnules and pinnae less crowded. As 

 these features appear to be constant, this form seems entitled to l)e considered 

 as a variety. 



