Maryland Geological Survey 305 



ThijStnfeldia rotundiloba Fontaine 



Plate XL, Fig. 3 



Thimifeldia rotundiloba Fontaine, 1890, Mon. U. S. Geol. Surv., vol. xv, 

 1889, p. Ill, pi. xxvii, figs. 6, 7. 



Description. — " Frond bipinnate or tripinnate ; principal rachis rather 

 stout; pinnules with thick texture, alternate, broadly ovate in outline, 

 obtuse, cut more or less deeply into subrhombic or broadly elliptical and 

 rounded lobes; nerves numerous, closely placed, slender but distinct, 

 repeatedly branching in the lower lobes, and diverging flabellately ; mid- 

 nerve in the terminal lobe dissolving in branches some distance below 

 the summit, and in its lower portion sending off very obliquely nerve 

 bundles or branches which fork one or more times.'' — Fontaine, 1890. 



This fragmentary species is of little specific or other value. It repre- 

 sents a form of rare occurrence and is very probably not specifically 

 distinct from Thinnfeldia granulata. 



Occurrence. — Patuxent FoRMATiOiSr. Fredericksburg, near Potomac 

 Run, Virginia. 



Collection. — IT. S. National Museum. • 



Thinnfeldia marylandica Fontaine * 



Plate XL, Figs. 8, 9 



Thinnfeldia marylandica Fontaine, 1906, in Ward, Mon. U. S. Geol. Survey, 

 vol. xlviii, 1905, p. 541, pi. cxiv, figs. 8, 9. 



Description. — " At the Arlington localities, and nowhere else, a num- 

 ber of fragments of a fern were found that seems to be a new species. 

 While the portions of the pinnse of this plant are not very rare, 16 in all, 

 they are so fragmentary 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, Goucher College, No. 5450, shows no more than a 

 portion of a detached ultimate pinna, or a lobed pinnule. This is repre- 

 sented in fig. 8. Fig. 9 gives two such fragments not so complete as that 

 given in fig. 8. These two, however, are so placed as to indicate that 



