34 THE OLDEE MESOZOIC FLOEA OF VIRGINIA. 



face of the shale, in some cases, with numbers of pinnae reduced almost to 

 threads, and present a peculiar aspect not easily described. As they do 

 not present any obvious points of difference from the normal A. microphjllus, 

 I have not thought it proper, in the absence of nervation, to separate the 

 plant, even as a variety. The fructification of none of these forms has 

 been seen. 



Formation and locality. — Rather rare at Clover Hill, in shaly sandstone, 

 associated with the main coal seam. 



Acrostichides densifolius, spec. nov. 

 « Plate X, Fig. 1. 



Frond bi- or tripinnate. Principal rachis slender, with a channel on the upper 

 side. Ultimate pinnse, -with channeled rachis, subopposite, closely placed, and imbri- 

 cated, Pinnules subopposite or alternate, separate to the base, closely placed and 

 imbricated, ovate-subfalcate, thin and membranaceous. Nervation very distinct, but 

 slender. Middle nerve stout at base, but dissolving into branches at the extremity, 

 inserted near the lower part of the pinnule. Lateral nerves going off obliquely, and 

 branched several times, the lower more frequently so than the upper. Fructified frond 

 not seen. 



The most characteristic features of this plant are the crowded pinnae 

 and pinnules, and the very distinct though slender nerves. Both the pinnae 

 of ultimate order and the pinnules overlap considerably. This overlap of 

 the pinnules is seen in the magnified pinnules, Plate X, Fig. 1 c. Plate X, 

 Figs, la, lb, show the nervation, which is of the kind characteristic of the 

 Virginia Acrostichides, and of the section of the genus with subfalcate pin- 

 nules. It will be seen that the shape of the pinnules here also tends to the 

 subrhombic form. 



This pla$H has a considerable resemblance to Acrostichides linncecefolius, 

 but this has a peculiar rounded form at the base of the pinnules, showing a 

 tendency to assume a heart-shape that is never seen in the plant now in 

 question, and besides A. linncecefolius is never imbricated in the pinnules. 



Formation and locality. — Very rare at Clover Hill, in strata associated 

 with the main coal. It comes probably from above the main coal, and in 

 connection with the series of small upper coal seams. It has never been 

 found anywhere but at Clover Hill, and only two or three specimens were 

 obtained. 



