32 THE OLDER MESOZOIC FLOEA OF VIRGINIA. 



In Plate XIV, Fig. 2, the fertile pinnules are well rounded, and the plant 

 is more slender than that represented in Fig. 1. 



The larger sterile pinnules of Acrostichides rhombifolius, those coming 

 from the lower parts of the frond, may be compared with two previously 

 described plants. These are Cyclopteris pachyrachis, Groeppert, from the Rhsetic 

 of Europe, and Neuropteris Schcenleiniana, Schimper, from the Trias. It is 

 a smaller plant than Cyclopteris pachyrachis in all respects, and especially 

 the rachises of the primary pinnae are much more slender. In the general 

 aspect of the plant it much resembles the fine fern from the Keuper which 

 has been so well figured by Dr. Schoenlein, and which Schenk has described. 

 It is, however, a more delicate plant than this, and the pinnules are decidedly 

 smaller. Still this fern of Dr. Schoenlein is perhaps its nearest relative 

 among described plants. 



Acrostichides rhombifolius is not very widely diffused. I have found 

 the sterile form at the Gowry Shaft, and very sparingly at Clover Hill. 

 Both sterile and« fertile forms occur rather abundantly at Carbon Hill in the 

 roof shales of the lower coal bed or the bed immediately below the main 

 seam. This seems to be the horizon of the plant everywhere. 



Formation and locality. — At Carbon Hill, at the Gfowry, and at Clover 

 Hill, over the lower coal bed. 



Acrostichides rhombifolius var. rarinervis. 

 Plate XIII, Fig. 3. 



The plant given in Plate XIII, Fig. 3, seems to differ from the normal 

 species, A. rhombifolius, sufficiently to separate it as a variety. The pinna? 

 are alternate, and have a very stout rachis in proportion to their size, and 

 it is bordered on each side by a raised line. The pinnules are smaller than 

 in the normal species, shorter and more nearly quadrilateral in form, with 

 the tips less produced. They are also more closely placed, and are fre- 

 quently imbricated slightly. The chief difference lies in the nervation, 

 which is more distinctly flabellate, and the branching of the nerves is less 

 frequent, giving fewer nerves in the pinnule. The upper pinnules are united 

 for some distance from the insertion, but the shape of the pinnules and their 

 nervation are features quite different from what we find in the united pin- 



