NOTES ON CHARACTERISTIC SPECIES. 



889 



and less broadly rounded or obtnse; lamina thick, sliohtly coriaceous, 

 a little concave along the middle, somewhat convex ventrally at the 



border. . . , 



Nervation rather coarse, distinct, regular, usually slightly in reliei, 

 more or less Habellate in all except the lowest pinnules or the lower part 

 of the largest ultimate pinnae; primary nerve but slightly dilTerenti- 

 ated in the small pinnules, or of moderate strength, vanishing near 

 the middle in those pinnules of intermediate size, or passing three- 

 fourths the length of the largest pinnules, decurrent in the smallest, 

 nearer the distal sinuses of the laterally unequal pinnules; nervilles 

 very oblique, often nearly equally close in all parts of the lamina, a 

 large portion springing directly from the rachis, especially in the 

 proximal half of the pinnule in all but the very large or the lowest 

 pair of pinnules, forking twice at a very narrow angle, one or more 

 of the divisions forking again even in the very small pinnules, usually 

 forking three times, sometimes four, in the largest pinnules, while 

 passing, with slight or sometimes no curvature in the smaller pinnules, 

 obliquely to the ..largin. 



The group of modifications or very nearly related forms which is 

 typified^ by the fern just described is at once the most predominant, 

 interesting, and complex in the fern flora of the entire Pottsville series. 

 The genus is typically distributed in the lower division of the Pottsville 

 serie^ of the Appalachian trough, and wherever fossil ferns are to be 

 found in that division some form or other of the group is present and 

 constitutes by far the most abundant, if not the exclusive, fern spe- 

 cies of the flora. Essentially this type is characteristic of the lower 

 division of the Pottsville, it being especially abundant in the vicinity 

 of the Pocahontas coal in the greatly expanded section of that for- 

 mation in southwestern Virginia. The distribution of the allied forms, 

 as well as the typical form, will receive special attention in another 



place. 



The typical form, described a1)ove, the illustrated specimens of 

 which were collected from the roof of the Pocahontas coal in the Flat 

 Top or Pocahontas coal field of southwestern Virginia and southern 

 West Virginia, is especially distinguished from the related forms of 

 the same 'group by its broadly attached or Callipteridioid pinnules 

 and the obliquity of its nervation, which is close, regular, coarse, and 

 derived in part from the rachis, the midrib being very poorly defined 

 in the small pinnules. Like the other forms from the basal portion of 

 the Pottsville series, it is essentially a Neuroatn!)>terk. This syn- 

 thetic character of the group of old Neuropterids in the earlier Potts- 

 ville is particularly important as indicating the connuon origin of the 

 genera Nenrupterl^, CalUpteridlum, and Miroiu^tira. Certain other 

 Neuropterids of the type of N. hlform,^, whicli is a typical Neu- 

 mlethopteris, similarly serve as connecting links between the genera 



