OLDER POTOMAC OF VllKilMA AND MARYLAND. 523 



RoGEUSiA ANGUSTiFOLiA I'ARVA Fontainc n. var. 



PL CXI, Fig. 9. 



At this locality fivo specimens of a dicotyledon were found that 

 indicate a smaller and narrower leaf than the normal Rogersia angus- 

 tl/olia. In fact, the leaves are so narrow that they suggest Cephalo- 

 taxopftis magnifolia." The nervation, however, although vaguely shown, 

 is that of a dicotyledon, and the leaf substance is thinner than that 

 of a Cephalotaxopsis. This may be a new genus, but the amount of 

 material is too small and the preservation too imperfect to permit the 

 estal)lishment of its full character. It may provisionally be regarded 

 as a variety of Rogersia angustifolia, which it resembles in all deter- 

 minable points except size. The specimen figured was collected by 

 Professor Ward in May, 1897. 



Rogersia lonoifolia Fontaine. 

 PI. CXII. Fig. 9. 



1889. Rogersia hnglfolia Font.: Potomac Flora (Monogr. U. S. Geol. Surv.. Vol. 



XV), p. 287, pi. cxxxix, fig. 6-; pi. cxliv, figs. 2, 2a, 2b; pi. el, lig. 1 : pi. dix, 



figs. 1, 2. 

 This is a plant which in the Virginia Lower Potomac is confined 

 to the Rappahannock horizon and appears to be represented by 4 

 fragments of leaves. Some of them are so poorly preserved as to be 



followed Feistmantel's method and described two species of Platyptorvgium (misspelling the name Plafyple- 

 rigium), P. densinerre and P. Rogersianum, to the former of which he doubtfully refers tlie specimen now 

 under consideration. 



As all the other forms that had prior to that date (1889), or have ever, been refernul to the subgenus 

 Platypterygium come from much older strata (Rhetic or at latest Jurassic), the placing of these Lower Cre- 

 taceous forms in that category must be prima facie questionable. It is of interest to note that Mr. Seward, 

 who examined tlie specimens "in the United States National Museum in 1897, makes, in his Jurassic Flora of 

 Yorkshire, p. 224, I'.KK), the following remark: 



"Attention may be drawn to the large leaves figured by Fontaine from the I'citomac plant lieds under 

 the name Plntiipkrigiiim densinerve. An examination of a few specimens of this species in the Washington 

 Geological Museum led me to regard the plant as probably a Nilssonia." 



It is true that Nilsonia is also a chi(-fly Jurassic genus, but undoubted forms of it occur in the Lower 

 Cretaceous even of America (see pp. 2.52, 253,254, 271, 284). The conjecture expressed in my letter to 

 Professor Fontaine when I sent him this specimen may therefore still prove not to have been so very wide of 

 the mark. At any rate, such forms are calculated to furnish crumbs of comfort to those who regard the 

 Potomac formation as Jurassic— L. F. W. 



« Monograph XV, pp 2HI), 237. 



