OLDER POTOMAC OF VIRGINIA AND MARYLAND. 541 



are strongly falcate, with nerves as a rule furcate from near the midrib. 

 The specimens of Dryopteris a?igustipinnata from the Arhngton localities 

 are small portions of ultimate pinnse, sometimes showing well-preserved 

 pinnules. One of the best specimens is shown in PL CXIV, Fig. 6. It 

 bears the number W. C, B., 5035. 



Dryopteris parvifolia (Fontaine) Knowlton. 

 PI. CXIV, Fig. 7. 



1889. Aspidium parvifolium Font.: Potomac Flora (Monogr. IT. S. Geol. Surv., Vol. 



XV), p. 100, pi. xxi, figs. 6, 6a, 6b; pi. xxiv, figs. 8, 8a; pi. xxv, fig. 10; 



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

 1895. Dryofteris ■parvifolia (Font.) Kn.: Bull. U. S. Geol. Surv., No. 152, p. 92. 



This species was described in Monograph XV, from ver^^ imperfect 

 small fragments, as coming from the Lower Potomac of Virginia. 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 be added to the diagnosis of 

 the species. 



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

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

 PI. CXIV, 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, B., 5059. 



Thinnfeldia marylandica Fontaine n. sp. 



PL 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 pinnae 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 would show 

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

 W. C, B., No. 5450, shows no more than a portion of a detached ultimate 



