98 THE POTOMAC OR YOUNGER MESOZOIC FLORA. 



nerve of the pinnules, and placed at the summit of the upper branch of a 

 forking nerve. 



Localities: Road-side near Potomac Run; 72d mile-post, near 

 Brooke ; rare. 



This fern is soni3thing like the living species Nephrod'min acntnm 

 Hook, and has no near affinity with any described fossil. As its sterile 

 form has not been found, its full character can not be made out. 



ASPIDIUM ANGUSTIPINNATUM, Sp. nOV. 

 Plate XVI, Figs. 1,3,8; Plate XVII, Fig. 1 ; Plate XIX, Fig. 10. 



Frond bipinnate or tripinnate, arborescent; in the sterile forms the 

 principal rachis is stout, straight, and rigid ; the ultimate pinnae alternate, 

 with a strong stiff rachis, linear-lanceolate, compOiratively short; [)innules 

 in sterile and fertile forms Pecopteris-like, closely placed, separate to the 

 base, opposite, rarely subopposite, linear, slightly falcate; leaf-substance 

 thick ; sterile leaves in the lower part of the frond denticulate, towards 

 the summit of the compound ultimate pinna; united and passing into 

 lobes ; midnerve of sterile and fertile pinnules continuing to the summit 

 of the pinnules; lateral nerves of the sterile pinnules of the lower and 

 middle portions of the penultimate pintuie furcate towards the base of the 

 pinnules and simjde towards their tips ; in the upper pinnules mostly sim- 

 ple, in the fertile pinnules furcate, and bearing the sori on the end of the 

 upper branches. 



In the fertile forms the principal rachis is comparatively slender, the 

 ultimate pinnse are opposite and widest towards their middle, and quite 

 long; the sori are placed on the margin of the pinnules, unlike those of the 

 preceding- species, which have them within the margin. The sori are com- 

 paratively large, reniform in shape, placed in a row on each side of the 

 midnerve, and in no case extend to the tips of the pinnules. They diminish 

 in numbers in passing from the pinnules of the lower part of the ultimate 

 pinnae to those of the upper portion, and disappear a little beyond the mid- 

 dle portion of the pinnae. 



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

 Canal; Fredericksburg; hill-side near Potomac Run. 



