OLDER POTOMAC OF VIRGINIA AND MARYLAND. 501 



occurs on the same slab and by the side of the fine specimen of Glypto- 

 strobus bi-ookensis shown on PL CX, Fig. 1, collected on October 16, 

 1892, at the Mount Vernon locality. The specimen is a fragment 45 mm. 

 long, which is depicted in PI. CIX, Fig. 7. Its maximum width, which 

 is at one end, is 16 mm. This widest portion seems to be the middle 

 part of the leaf. It narrows toward the opposite end, but the true 

 termination does not seem to be preserved. When entire, the leaf was 

 probably narrowly elliptical in form. It looks somewhat like a Rogersia, 

 but does not have the nervation of that plant. So far as it can be made 

 out, the nervation is peculiar. At the wider end, and for some distance 

 toward the narrower, there is an imprint along the central line of the 

 leaf that ma}^ represent a midrib, but it is ill defined, and seems to be 

 composed of several slender nerves that wei'e loosely united, and which 

 now, under the pressure to which the leaf has been subjected, have 

 become separated in a straggling manner. Before reaching the narrow 

 end of the leaf the apparent midnerve abruptly ends, seeming to split 

 up. The other nerves, on each side of the ones just described, are faint 

 and irregular, and their course can not be certainly made out. They 

 seem to run approximately parallel with the central nerve and to 

 anastomose, forming long straggling meshes. The plant is veiy rare. 



SCLEROPTERIS VERNONENSIS Ward. 



PI. evil, Fig. 10. 



1895. Scleropteris vernonensis Ward : The Potomac Formation (Fifteenth Ann. Rep. 

 U. S. Geol. Surv., 1893-94), p. 349, pi. ii, figs. 1, la, 2, 3. 



Professor Ward in his paper on the Potomac formation, page 349, 

 has described this plant, and on pi. ii, figs. 1, la, 2, 3, has figured some 

 of the forms. The specimen depicted in fig. 3 is the largest one found. 

 Thirteen other scattered fragments occur in the Mount Vernon collec- 

 tions, but they are mostly small bits of ultimate pinnae, showing at most 

 a few pinnules. The texture of the pinnules is thick and leathery, so as 

 to hide the nerves. In fig. 1, la, enlarged. Professor Ward has given a 

 form of this plant which differs from the normal, and which is apparently 

 its fructified form. One specimen, depicted on PI. CVII, Fig. 10, occurs, 

 which is larger than the minute specimen given by Professor Ward in 

 fig. 1, and which indeed is nearly as large as the magnified figure. 



