ACROSTICHOPTERIS. 61 



most features stands nearest to Acrostichum, much resembling the 

 section Rhipidopteris. In this latter, however, the fructification 

 is borne on separate pinnules. If we place the fructified pinnules 

 of Rhipidopteris as basal segments on the sterile ones, we have 

 a form strikingly like Acrostichopteris. The genus has also some 

 resemblance to Marsilea" 1 



It is doubtful if the generic name Acrostichopteris be the most 

 suitable for such specimens as the English rocks have afforded. 

 In Fontaine's specimens there is some evidence as to fructification 

 characters, but in the few fragments from Ecclesbourne there 

 are no traces of fertile leaves. The similarity, however, between 

 the American and English specimens appears to be exceedingly 

 close, and the habit represented by the various species is not one 

 which occurs very commonly among recent genera. 



In the recent species Acrostichum peltatum, Sw., 2 the sterile 

 leaves have the same deeply divided pinnules with narrow segments 

 as those of A. Ruffordi, but in the latter form there are several 

 pairs of pinnules attached to one axis; the difference in the 

 arrangement of the fertile pinnules has already been alluded to 

 by Prof. Fontaine. 



It is difficult to determine whether such specimens as those 

 described below should be spoken of as pinnse of a frond with a 

 creeping rachis, or as the pinnate leaves of a creeping rhizome, 

 as in Acrostichum peltatum. I have placed the genus in the Poly- 

 podiacea on the strength of Fontaine's conclusions, drawn from 

 much more complete material than the British Museum affords. 

 The evidence as to family characters is best seen in the figures 

 of American specimens ; it is by no means all that could be desired. 



1. Acrostichopteris Ruffordi, sp. nov. 



Type. Pinna3 and portions of rachis. In the British Museum. 



Main rachis probably creeping, bipinnate, pinna? linear ; pinnules 

 alternate, rhomboidal or cuneate, deeply divided into narrow 

 cuneate segments with acute or obtuse teeth. Venation of the 

 Ctenopteridis type. No fructification preserved. 



1 Potomac Flora, p. 106. 



2 Fee, Genera Filicum, pi. ii. 



