70 THE OLDER MESOZOIC FLORA OF VIRGINIA. 



centimeter wide, and gradually tapering towards the summit, where it is rapidly nar- 

 rowed, and terminated by a single leaflet; sometimes an abrupt narrowing occurs 

 some distance below the summit ; irregularly striate, and bordered on each side of the 

 upper surface, by a raised margin formed by the insertions of the thickened bases of 

 the leaflets, flat in the central portions, and apparently rather fleshy. Leaflets attain- 

 ing an extreme length of 10 centimeters, average length, 6 to 8 centimeters ; width in 

 middle, 1£ to 2£ millimeters, slightly expanded at base, and towards the summit 

 tapering slightly, and bluntly rounded off, alternate, or subopposite, variously attached 

 according to position, those at the base of the leaf going off often nearly or quite at a 

 right angle, those in the middle, under an angle of about 45° and slightly curved up- 

 wards, those towards the summit of the leaf, under a more and more acute angle, until 

 the terminal leaflet stands in the prolongation of the axis of the midrib. The lower 

 leaflets which stand at right angles, or at a large angle, are usually separate, and 

 sometimes remote, and not decurrent, those of the middle part of the leaf are separate 

 to the base, and sbghtly decurrent, those of the upper part are united at base and 

 strongly decurrent, all are thickened and more rigid at base, forming a raised line on 

 the margin on each side of the midrib. Nerves strong, and slightly thickened at base, 

 single, parallel to one another and to the margin of the leaflets, central nerves of the 

 leaflets going off at right angles to the midrib, or under the same angle as the leaflet, 

 the lateral ones leaving under an acute angle ; about six in number, of which one or 

 two are stronger than the rest; generally the central one is stronger when the in- 

 equality exists. 



This splendid plant stands third in the abundance of its individuals and 

 the area over which it is diffused. It is often found with Macrotceniopteris 

 magnifolia 'as its sole companion, or with that plant along with Equisetum 

 Bogersi. A fine-grained gray shale, not far above the main coal, is espe- 

 cially noteworthy for the thousands of imprints of this plant, along with 

 the Macrotceniopteris, which occur in it, with almost never any other fossil. 

 The great numbers of imprints of this plant, and the good preservation of 

 many of them, enable me to make a very satisfactory study of it. It will 

 be seen that within certain limits it is quite polymorphous. Fragments 

 have been seen which indicate that the entire leaf, with its petiole, in the 

 case of the largest specimens, could not have been much under a meter in 

 length. The petiole must, in the largest specimens, have been considerably 

 over 20 centimeters in length. Fragments of it 10 to 15 centimeters long 

 occur in the gray shale. The width of the petiole of the largest leaves was 

 at least one centimeter. The petiole was bare of leaflets, as is represented 

 in Plate XXXVII, Fig. 1 a, which is a fragment of natural size, of a specimen 

 about 15 centimeters long, which occurred on the same piece of shale with 



