Maryland Geological Survey 359 



The existing genus Bowenia has analogously divided fronds, while a 

 number ef existing species of Encephalartos have similarly toothed 

 pinnules. 



Occurrence. — Patuxent Formation. Fredericksburg, Virginia. 



Collection. — U. S. National Museum. 



Genus NILSONIA Brongniart 

 [Ann. Sci. Nat, tome iv, 1825, p. 218] 



This genus was founded by Brongniart for certain remains from 

 the Eheetic of Sweden which had been recorded and figured by Nilsson 

 in 1820 who regarded them as fern remains. In the Prodrome the 

 diagnosis is as follows : 



" Feuilles pinnees ; pinnules rapprochees, oblongues, plus ou moins 

 alongees, arrondies au sommet, adherentes au rachis par toute la largeur 

 de leur base, a nervures paralleles, dont quelques-unes sont beaucoup plus 

 marquees." ^ 



The genus was regarded by Brongniart as referable to the Cycadales, 

 a view generally accepted by subsequent workers,' although Schenk"* 

 in 1867, on the basis of supposed sori on some german specimens, 

 referred it to the Filicales, in which he was at first followed by Schimper * 

 and more recently by Solms-Laubach.* 



The genus has also been ably discussed by Saporta, Kathorst, Seward, 

 and others, Nathorst in particular having shown that the two kinds of 

 veins supposed to occur together were due to slight folds in the lamina 

 due to pressure, maceration, or the creep of the enclosing strata. He 

 characterizes the veins as equal and simple, and emphasizes the insertion 

 of the lamina on the upper surface of the rachis, suggesting that Schenfs 

 supposed sori are fungal or stomatal in their nature. ° 



^Brongniart, Prodrome, 1828, p. 95. 



^ Sclienk, Die fossils Flora Grenzschichten Keupers u. Lias Frankens, 1867, 

 p. 124. 



= Schimper, Pal. V€get., tome i, 1869, p. 488. 



* Solms-Laubach, Fossil, Botany, 1891, p. 139. 



' See Nathorst, Ueber die gattung Nilssonia Brongn., Kongl. Svenska Vet. 

 Akad. Handl., Band xliii, 1909, No. 12. 



