150 THE POTOMAC OR YOUNGER MKSOZOIC ELORA. 



Jurassic in type. In Fig. 14, the lowest pinnule on the right-hand side 

 belongs to the left hand, and forms the outermost one on that side. It has, 

 by displacement and pressure, been turned to one side and doubled back 

 under the summit of the stipe, so as to lie alongside of the outermost one of 

 the right-hand side of that frond. 



Sagenopteris Virginiensis, sp. nov. 



Plate CXXXVIII, Fig. 13; Plate CXXXIX, Fig. 1. 



Frond unknown; shape of pinnules not seen, probably broadly ellip- 

 tical or oval; stipe or petiole of pinnules apparently long; midnerve toward 

 the base very strong, dissolving in branches towards the apex ; areolation 

 very distinct, formed by lateral nerves which go off obliquely and curve 

 outwards to meet the margin, forking repeatedly, and anastomosing to form 

 meshes that are irregular in size and shape, being mostly elongate, oblong, 

 or subrhombic. 



Locality: Fredericksburg; very rare. 



Plate CXXXVIII, Fig. 13, seems to represent the upper part of the 

 specimen figured in PI. CXXXIX, Fig. 1. The lamina of the leaf in the 

 lower part of this specimen has been torn away, leaving the midrib bare. 

 This appears to be a very large species of the genus. 



SCLEROPTERIS, Saporta. 



Frond bipinnate or tripinnate, coriaceous ; pinna? pinnately parted, 

 pinnules or segments more or less constricted at base, decurrent on the 

 lower side, and forming a narrow wing to the rachis, entire, or incised and 

 lobed on the anterior margin ; nervation immersed, formed of a few nerves 

 branching flabellately from a common nerve at the base, diverging flabel- 

 lately by repeated branching to fill the limb. 



The above is very nearly Saporta's diagnosis of the genus Scleropteris 

 established by him. I modify the nervation only so as to include the 

 forms described in the next following pages, which clearly belong to this 

 genus. As to the nervation, Saporta says, in Pak'ontologie Frah(jaise, 

 Plantes Jurassiques, vol. 1, page 365, that the nerves come out obliquely 

 from the back side of the pinnules. This is not the case in all specimens, 



