OLDER POTOMAC OF VIRGINIA AND MARYLAND. 517 



locality on the day named belong to the fern Thyrsopteris rarinervis, but 

 some tubers of Equisetum marylandicum and some other Thyrsopteris 

 forms also occur. The plants from the locality on the west side are all 

 different from these, no ferns having been found there, but a cone probably 

 of Sphenolepidium virginicum, a leaf of Dioonites Buchianusf, and one of 

 Baieropsis longvfolia were found. 



On October 2, 1892, Professor Ward and Doctor Hollick collected at 

 the first-named locality a number of specimens, but nearly all of them 

 belong to Equisetum marylandicum. 



On July 7, 1893, I went to this same place with Professor Ward and 

 we secured a few specimens, but they were mostly different from any 

 previously collected, including a species of Brachyphyllum. This shows 

 that the different clay seams hold different plants, and that the flora of 

 these beds is very rich and varied. 



The following species occur in all these collections : 



Baieropsis longifolia Font 1 specimen. 



Brachyphyllum parceramosum Font. ? 3 specimens. 



Cladophlebis Browniana (Dunk.) Sew 1 specimen. 



Dioonites Buchianus (Ett.) Born. ? 1 specimen. 



Equisetum marylandicum Font .. 19 specimens. 



Onychiopsis psilotoides (Stokes & Webb) Ward 1 specimen. 



Sphenolepidium virginicum Font. ? 1 specimen. 



Thyrsopteris densifolia Font 1 specimen. 



Thyrsopteris divaricata Font. ? 2 specimens. 



Thyrsopteris elliptica Font 3 specimens. 



Thyrsopteris nervosa Font 3 specimens. 



Thyrsopteris rarinervis Font 60 specimens. 



Zamiopsis insignis Font. ? 1 specimen. 



Most of the specimens from the new reservoir seem to have been 

 reduced to small fragments, but in many cases they are pretty well pre- 

 served, for the leaf substance is often retained 



Equisetum marylandicum Fontaine. 



PI. CIX, Fig. 10. 



1889. Equisetum marylandicum Font.: Potomac Flora (Monogr. U. S. Geol. Surv., 

 Vol. XV), p. 65, pi. ii, figs. 10, 10a. 



This species stands second in abundance at this locality, and a good 

 many specimens were obtained. It is a peculiar fact that nearly all of 



