1 56 THE POTOMAC OR YOUNGEE MESUZOIC FLOEA. 



The Potomac fossils give more of tlie frond than the species hitherto 

 known, and thns add a good deal to our knowledge of this curious genus. 

 Unfortunately no trace of fructification was seen. 



Ctenopteris insignis, sp. nov. 



Plate LXr, Figs. 4, 5 ; Plate LXII, Fig. 1 ; Plate LXIIF, Figs. 1, 2. 



Frond large, arborescent, bipinnate or tripinnate ; principal rachis 

 very strong, striate; ultimate pinufe with strong rigid rachises, alternate, 

 terminating in a lobed segment, the pinnules j^assing into lobes more or 

 less united towards the ends of the ultimate pinn;T3; pinnules thick and 

 leathery, those of the lower and middle portions of the pinna; attached by 

 the entire base, slightly decurrent, separate, cut away obliquely above, 

 alternate to subopposite, gradually diminishing towards the summit of the 

 pinnae in size and depth of toothing, not sensibly narrowed at base, oblong- 

 acute, curved slightly forward, terminating in a large ovate to subtriangu- 

 lar acute tooth. The pinnules usually show two acute or spinous teeth on 

 each side, a couple near the base, and a second couple near or at the sum- 

 mit of the pinnule, the associated members of the couples being opposite 

 or subopposite. Sometimes there is an additional tooth on the posterior 

 margin below the upper one, and sometimes the terminal tooth is enlarged 

 to an oblong lobe (see PI. LXI, Fig. 4), which is slightly notched; nerves 

 several, depai'ting separately from the principal rachis along the entire 

 width of tlie base of the pinnule, the outermost ones once forking and 

 curving outwards, the inner ones forking deeply several times and slightly 

 diverging flabellately, the ultimate branches nearly or quite parallel, long, 

 and slender. 



Localities: Fredericksburg; road-side near Potomac Run. 



This splendid plant is not uncommon at the first-named locality, and 

 is found in small bits only at Potomac Run. All the specimens figured 

 come from Fredericksburg. The specimens show a black, glossy plant- 

 matter, which peels off" like paper from the stone, and indicates that the epi- 

 dermis was dense and durable. A thick coriaceous epidermis covered the 

 main rachis and all parts of the plant. The nerves are not usually dis- 

 tinctly seen, being obscured by the tliick epidermis. The form given in 



