OLDER POTOMAC OF VIRGINIA AND MARYLAND. 525 



TnYiisopTERis nF.ri'nuF.xs Fontaine. 



PI. CXI, Fit,'. II- 



1889. Thyrsopferis dccurrens Font.: Potonuu- Flora (Monogr. U. S. Gcol. Siirv., 

 Vol. XV), ]). l.'5(), pi. xiiii, (ii;.s. 7, 7a; |)1. .\lvi, (iffs. 2, 2a, 4; \)\. xlix, iigs. ,3, 

 5a, 6, (ia, 7. 



Only Olio specimen of this fern was found at tlio Langdon locality. 

 It occurs in the collection nuule h}' Professor Ward in May, 1897. It 

 consists of the u|)|)Ci- part of a compound pinna and may l)e compared 

 with the .specnnen represented by fig. 7 of pi. xlix of Monograph XV. 

 It is shown on PI. CXI, Fig. 11. This species has a wide range in the 

 Virginia Potomac. 



Zamiopsis ixsignis Fontaine, 



PI. CXIII, Fi-xs. 4, :->. 



1889. Zamiopsis insigiiis Font.: Potomac Flora (Mono<z;r. U. S. Geol. .Surv., \'ol. 

 XV), p. 1()2, pi. Ixii, fig. .H; pi. Ixiv, fig.s. 1, A; pi. Ixv, figs. 4-6; pi. Ixvi. 

 fig. 2: pi. Ixvii, tig. 7. 



Two impressions of a plant were found that belong to Zamiopsis 

 irisignis. This remarkable plant is highly characteristic of the lowest 

 strata of the Lower Potomac of Virginia. At the time of the preparation 

 of Monograph XV it had been found only at the Fredericksburg locality, 

 but since that time it has been discovered in abundance near Alexandria, 

 in the l)asal beds at Chinkapin Hollow. This is a type that is easily 

 detected even in small fragments. The specimens show portions of 

 ultimate piniue. The form given in PI. CXIII, Fig. 4, conies from lower 

 down on the plant, where the pinnules are larger. Several of these are 

 shown. The form given in fig. 5 is the terminal portion of an ultimate 

 pinna, where the pinnules are narrow and show only the characteristic 

 toothing of the plant. The distribution of this species is geologically so 

 well defined that the plant is especially valuable to fix the horizon of 

 the strata in which it occurs. 



Both the specimens were found by Professor Ward in May, 1897. 



(!E.\ER.4I, REMARKS. 



The account of the plants given above makes it evident that the 

 locality yielding them is on the horizon of the basal beds of the Potomac 



