no. 1769. FOSSIL PLANTS OF THE POTOMAC GROUP BERRY. 633 



linear-lanceolate, apex acute or occasionally obtuselj terminated; a 

 well-marked midrib from which lateral veins arc given oil' eh her at right 

 angles or more or less obliquely; these may be unbranched or acutely 

 forked as they pass toward the leaf margin."" The relation of the 

 simple species to those with pinnate fronds is uncertain, although it 

 seems probable thai they all belong to the same stock. It proves to 

 be an almost impossible task in the absence of any but the best pre- 

 served material to distinguish between Tseniopteris-like forms and 

 the remains of such a cycadaceous genus as Nilsonia. The lateral 

 attachment of the lamina in the former and its superior attachment 

 in the latter are characters which are very often obscured in the proc- 

 ess of fossili/ation and the usual segmentation of the Nilsonia fronds 

 is also a character which is not constant. 



The genus is abundant in the late Paleozoic, the Paleozoic forms 

 having been discussed by Zeiller, White, and others, the latter author 

 pointing out'' their probable filiation with the Megalopteris stock, 

 which extends back to the Middle Devonian. Species of Tseniopteris 

 are abundant during the Mesozoic and occasional occurrences are 

 recorded during the Cenozoic. It maybe seriously questioned, how- 

 ever, whether the Paleozoic and post-Paleozoic Tamiopterids belong 

 to the same stock 



In the Potomac group several species have been described under the 

 genus Angiopteridium which it has seemed best to refer to Tseniopteris 

 in the absence of all traces of fructification and the consequent lack of 

 certainty regarding their taxonomic position. Species also occur in 

 the Shasta beds of California and probably in the Kootenai of Mon- 

 tana and British Columbia. It is also a common type in the Euro- 

 pean Wealden. 



Regarding the botanical affinity of the various forms of Tseniopteris 

 it seems very probable that the bulk of them are closely related to the 

 Marat fiacea\ a family with which they are allied by nearly all of the 

 authors mentioned. In fact most authors ally them directly with 

 living genera, thus Schimper c positively refers the Kinetic species 

 Tseniopteris munsteri to the modern genus Marattia, a conclusion 

 which it is difficult to dispute after seeing the magnificent fruiting 

 specimens figured by this author. Schenk, d on the other hand, thinks 

 this species Is closest to Angiopteris, while Raceborski, from the: study 

 of fruiting specimens from Poland, which he identifies with this same 

 species, is equally sure of the correctness of Schimper's conclusions. 

 To mention one or twoot her instances, Schenk' is sure that Danaeopsis 



" Seward, Wealden flora, pi. I. L894, p. 124. 



& White, Bull. Geol. Sue. A.mer., v., I. I, L893, pp. J J i * L32. 



cSchimper in Zittel'a Handbuch, L890, p. 



dSchenk, Die foss. Pflanzenreste, L888, p. 30 



cldem, p. :'.">. 



