Maryland Geological Survey 391 



The genus has been ably discussed in its Mesozoic aspects by Saporta, 

 Zigno, Schenk, Schimper, Seward, and other authors, the former espe- 

 cially, while following Broiigniart's original characterization of fronds 

 usually simple, considerably extends liis diagnosis/ Saporta's diagnosis 

 is quoted in a recent work by Seward" and need not be repeated. The 

 latter author uses the genus in a wide sense following ISFathorst in in- 

 cluding under it such other genera as Oleandridium, Angiopteridium, 

 Marattiopsis, Danceopsis, etc., in which the evidence of relationship seems 

 insufficient for the use of names implying affinity with the respective 

 modern genera. His characterization may be quoted with profit: 

 " Frond simple or pinnate, usually lanceolate or linear-lanceolate, apex 

 acute or occiisionally obtusely terminated; a well-marked midrib from 

 which lateral veins are given off either 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 they may possibly all belong to 

 the same stock. It proves to be an almost impossible task in the 

 absence of any but the best preserved 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 process of fossilization 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 hav- 

 ing been discussed by Zeiller, White, and others, the latter author point- 

 ing out* their probable filiation with the Megalopteris stock, which ex- 

 tends back to the Middle Devonian. Species of Tceniopteris are abundant 

 during the Mesozoic, and occasional occurrences are recorded during the 

 Cenozoic. It may be seriously questioned, however, whether the Paleo- 

 zoic and post-Paleozoic Tseniopterids belong to the same stock. 



In the Potomac Group several species have been described under the 



^ Saporta, PI. Jurass., tome i, 1873, p. 430. 



^ Seward, Wealden Flora, pt. i, 1894, p. 122. 



3 Seward, Wealden Flora, pt. i, 1894, p. 124. 



' White, Bull. Geol. Soc. Amer., vol. iv, 1893, pp. 119-132. 



