260 Systematic Paleontology 



The genus Dryopterites may be defined as follows : Fronds large, bi- or 

 tripinnate or pinnatifid, pinnules dentate, crenate, lobate, or entire, 

 attached by their whole base or slightly constricted basally. Venation 

 of the Cladoplilebis type, the single midrib becoming attenuated distad 

 by the branching off of numerous simple or forked lateral veins. Sori 

 not elongated, but elliptical, circular or reniform in outline, borne in a 

 single row on either side of the midvein toward the end of a lateral vein 

 or on a distal branch of a lateral vein. Minute structure not discernible. 



The genus Dryopteris has upwards of four hundred existing species of 

 wide geographical distribution and consequent difference in size, form, 

 and habit. Of these about 35 occur in North America. The fossil species 

 which have been referred to Dryopteris number upwards of fifty forms 

 and include about 18 from the Lower Cretaceous, six from the Upper 

 Cretaceous, and about twenty from the various Tertiary horizons. 

 Schimper,^ in 1869, in treating the then known fossil species, referred 

 to Aspidium, as Dryopteris was then called, refers all but two from the 

 relatively recent Upper Miocene (Tortonian) to the form genus Pecop- 

 teris. 



The eighteen species just mentioned from the Lower Cretaceous in- 

 clude fourteen from the Potomac Group, which Professor Fontaine so 

 identified. These have been found in a number of instances to be iden- 

 tical with remains referred to CladopJilehis, with which they have been 

 united whenever the evidence warranted such a course. After this proc- 

 ess of elimination there remained the following six, more or less illy 

 defined, types which are here referred to Dryopterites, as indicative of 

 their resemblance both in form and soral characters, as far as these are 

 decipherable, to Dryopteris. 



The writer is strongly of the opinion that the following forms are 

 closely allied to some of those which are discussed under Cladoplileiis, 

 and perhaps several are identical with such forms. The materials are, 

 however, so sca.nty, poorly preserved, and inconclusive that a conserva- 

 tive course demands that they be kept separate. 



^ Schimper, Pal. Veget., tome i, 1869. 



