OLDKK POTOMAC OF VllUilMA AND MAKVLAND. 541 



are strongly falcate, with iici'vos as a I'ulc furcate fi'oiii near the niidi'ili. 

 The specimens of Dryujdcris angustii)})niata from the Arlington localities 

 are small portions of ultimate pinna\ sometimes showing well-preserved 

 pinnules. Owe of the best specimens is shown in PI. CXIV, Fig. 6. It 

 bears the nmnber W. ('., B., 5035. 



DuYOPTKHis i'Ai;\ noil A (l''()ntaiM(') Kiiowltoii. 

 ri. t'XI\'. Ki<,'. 7. 



1889. Aspidiurii ]>(nrifolium Font.: Potoinac Flora (Monoj;!-. I'. S. Oool. Surv., Vol. 



XV). J). 100. pi. xxi, figs. (i. (ia. (ih: pi. xxiv, tigs. S, Na; j)l. xxv. tig. 10; 



pi. xxvi, figs. 1. la, 14, 16, Kia. 17, 

 1805. Iliijopfnis pdrri/olld (Font.) Kn.: P>iill. F. S. Gcol. Surv., No. lo'i, p. <)2. 



This species was desci'ibed in Monograph XV, fioin very iinpei'fect 

 small fragments, as coming from the Lower Potomac of \'ii-ginia. The 

 amount of material from the Maryland Potomac is much larger and some 

 of the fragments of this fern found in it are larger than any of the Virginia 

 specimens, but still nothing but small portions of the plant were found. 

 For this reason nothing of importance can l)e added to the diagnosis of 

 the .species. 



This plant, like the two forms of Ckulophlebis acuta, is in Maryland 

 confined to the Arlington localities, where 70 specimens of it were obtained. 

 PI. CXR\ Fig. 7, shows the most complete form found. It is a consid- 

 erable portion of a penultimate pinna with many imperfect ultimate 

 pinnse, and on many of the latter good pinnules are found. It bears the 

 number W. C\, R., 5059. 



Thinnfeldia marylandica Fontaine n. sp. 



PI. CXIV, Figs. 8, 9. 



At the Arlington localities, and nowhere else, a number of fragments 

 of a fern were found that seems to be a new species. While the portions 

 of the pinna' of this plant are not very rare, 16 in all, they are so frag- 

 mentary that it is difficult to make out its character. On the whole, it 

 agrees best with the genus Thinnfeldia, so far as can be determined from 

 the imprints. Still, it is quite possible that better specimens woidd show 

 that it belongs to some other genus. The most complete specimen, 

 W. C, B., No. 5450, shows no more than a j)ortion of a detached ultimate 



