A REVISION OF THE FOSSIL PLANTS OF THE GENERA 

 ACROSTICHOPTERIS, T.EXIOPTEIUS, NILSONIA, AND 

 SAPIXDOPSIS FROM THE POTOMAC GROUP. 



By Edward W. Berry, 

 Of the John* Hopkins University, Baltimore. 



The present paper is the second of a series of revisions of the more 

 important genera of fossil plants from the Potomac group in Maryland 

 and Virginia. The first dealt with the genus Nageiopsis and formed 

 No. 1.738 of the present volume of the Proceedings. The material 

 upon which these studies are based is nearly all contained in the U. S. 

 National Museum collections, but the collections of the Johns Hopkins 

 University and the Maryland Geological Survey have also been 

 utilized. 



The following pages are devoted to the genera AcrosticJiopteris, 

 T;i nlojitcrts, Xilsonia, and Sapindopsis. Of these the fern genus 

 AcrosticJiopteris and the dicotyledonous genus Sapindopsis were 

 founded upon collections from the Potomac strata to which they are 

 largely confined. The fern genus Tseniopteris and the cycad genus 

 Xilsonia have not been previously recognized in the Lower Cretaceous 

 of eastern North America, the specimens upon which the present 

 determinations are based having been previously wrongly correlated 

 with the genera Angiopteridium, Anomozamites, and Platypterigium. 



THE GEMS ACROSTICHOPTERIS OF FONTAINE. 



This genus is characterized as follows by its describer: 



Frond.- probably creeping, with very long, often flexuous rachises, which seem to 

 have been more or less succulenl ; pinnae going off obliquely, long and apparently blen- 

 der; nit iniate pinnae or pinnules subopposite to alternate, comparal ively short, and cut 

 down nearly I" the rachis into more or less cuneate flabellate pinnules or primary seg- 

 ments. These are divided generally into cuneate llahellate segments, which in turn 

 are separated into oblong segments ending in oblong, or ovate-obtuse, or acute teeth; 

 pinnules decurrenl and forming a wing; nerves slender but distinct, llabel lately diverg- 

 ing, forking dichotomously, ami ending in the teeth; fructification occurring on the 

 basal segments of the pinnules, in the upper porl ions of tin • frond on the upper one alone, 

 in the lower portions on the upper and lower ones, the fructified segments close ap- 

 pressed to the principal rachis. The fructified segments are so modified as to take the 



Proceedings U. S. National Museum, Vol. 38— No. 1769. 

 Proc. N.M.vi >l.:;s— 10 -iu 625 



