46 THE OLDER MESOZOIO FLORA OF VIRGINIA. 



insertion, and the long, thread-like branches are so closely crowded together 

 that, without the help of a lens, they often appear to be single nerves. 

 This nervation is shown in the magnified pinnules given in Fig. 1 a, which 

 represents two pinnules of Fig. 1» Plate XXIV, Fig. 3, represents a com- 

 pound pinna of the more common kind, and Fig. 3 a gives enlarged pinnules 

 of the same. Figs. 4, 5 represent portions of two very long ultimate pinnse, 

 perhaps from lower down on a compound pinna, like that in Fig. 3. Fig. 

 5a is a magnified pinnule of Fig. 5, and Fig. 4« a magnified pinnule of Fig. 

 4. Plate XXI, Fig. 4, represents the upper portion of a compound pinna 

 corresponding to that represented in Plate XXIV, Fig. 3 ; and Plate, XXI, 

 Fig. 3, gives the extremity (magnified) of an ultimate pinna of the same. 



Formation and locality. — The plant is found only at Clover Hill, in 

 shales associated with the highest of the series of small coal seams, above 

 the main seam. 



Asterocarpus platyrachis, spec. nov. 



Plate XXV, Figs. 2-6; Plate XXVI, Fig. 1. 



Frond bi- or tripinnate, perhaps arborescent. Principal rachis rigid and stout, 

 one centimeter and more in diameter. Ultimate pinnae alternate or subopposite, with, a 

 broad flat rachis. Sterile and fertile pinnules different, sterile pinnules ovate oblong, 

 bluntly rounded at the extremities and slightly falcate, united for some distance above 

 the bases. Nervation Pecopteris-like, midrib strong and distinct to near the end, and 

 then splitting into branches. Lateral nerves very distinct, going off obliquely, fork- 

 ing near the midrib, the two branches diverging slowly, and continuing nearly par- 

 allel to one another until they meet the margin of the pinnule. Pinna? of the upper- 

 most part of the primary pinna or frond, passing through lobed pinna? into simple 

 pinnules. These latter near the summit of the frond are much reduced in size, and 

 are united more and more, reproducing the form of the pinnules of the lower part of 

 the frond. Fertile pinnules, without lateral nerves, having a stout rigid midrib, with 

 large sori placed on the margin of the pinnules, and covering most of their surface, form- 

 ing a row on each side of the midrib, and each row gradually approaching the other 

 towards the summit of the pinnules, forming thus a pinnule elongate-triangular in 

 shape. More rarely fertile and sterile pinnules occur together on the same pinna. The 

 sori are formed of four or five sporangia, which usually appear to be consolidated at 

 their bases, but at their summits are separate and grouped radially around a central 

 point. 



The sori are very large and prominent, placed on the margin of the 

 narrowed fertile pinnules, and occupy most of their surface. The two rows 

 approach each other towards the summit of the pinnules, and are capped 



