70 THE POTOMAC OR YOUNGER MESOZOIC FLORA.. 



like Pccoi)teris Ilaibuniensis, L. and H., from the Oolitic formation of Ilai- 

 burn Wyke, Yorkshire, England, than any other previously described 

 plant, but is quite distinct from this. It has some resemblance to Neiirop- 

 teris undulata, L. and H., Foss. Flor., vol. 2, PI. LXXXIII. 



Cladophlebis Virginiensis, sp. nov. 



Plate III, Figs. :i-8 ; Plate IV, Fig. 1, 3-G. 



Frond bipinnate or tripinnate, arborescent; principal rachis very 

 stout and woody ; rachises of the penultimate and ultimate pinnae stout, 

 rigid, on tiie under side rounded and prominent, on the upper side ridged 

 on each margin ; ultimate pinnaj very long, rather remote, subopposite ; 

 pinnules alternate to subopposite, at the tips varying from acute to obtuse, 

 with margins usually very entire, rarely crenulate to subdentate, in shape 

 ovate to lanceolate and subfalcate, attached by the greatly widened base, 

 mostly separate to the base ; midnerve stout at base, but soon becoming 

 attenuated, and some distance below the summit splitting- up into veins ; 

 lateral nerves at the base of the pinnules branched several times, in some 

 cases forming nerve-bundles, in ascending towards the tips of the pinnules 

 less and less subdivided, finally simply furcate and unbranched. 



Locality: Fredericksburg. 



This splendid plant is perhaps the most common fern at Fredericks- 

 bui'g, but it is not abundant there. Tlie specimens are usually quite frag- 

 mentary, as if they had been transported some distance. From the size 

 of the rachis shown in PI. Ill, Fig. 3, the plant must have been arbor- 

 escent. The rachis of the pinnag in all the specimens is strong and rigid. 

 The under side of the rachis is usually rounded and prominent. On its 

 upper surface a strong ridge is often seen on each margin, and to this the 

 pinnaa and pinnules are attached. The pinnules of PI. Ill, Fig. 3, may be 

 taken as typical for form and dimensions. Sometimes, however, pinnules 

 may be seen which are quite obtuse at their tips, and in some cases they 

 occur with margins showing incipient lobiiig. These come probably from 

 lower portions of the frond. Possibly in PI. IV, Figs. 1, 3, may be de- 

 noted a smaller species of this type. 



