890 FLORAL ZONES OF THE POTTSVILLE FORMATION. 



Xenropteru and Alethojyteris. The subject of the origin and relations 

 of these genera to Megalopteria and other Paleozoic types has Ijeen 

 discussed by me in connection with the description of a somewhat 

 composite form from the Des Moines series of Missouri/ 



The pinnules of the typical Xewy/ptcris Pocahontas are, in general, 

 rather broadl}' ovate when small, and rounded at the top. The form of 

 the terminal pinnules of the younger pinnte resembles that of the true 

 X. SmitJisll as originally described and figured from Alabama, but the 

 latter is considerably smaller and less sublobate, besides l)eing rather 

 narrower. The species in hand is in reality readily distinguished from 

 X. Smithsuhj its generally larger pinnules, which are broadly attached, 

 more ovate, instead of oval or nearh?^ round, when small; by the far 

 less developed median nerves, and especially by the much less curved 

 nervilles, which are oblique, springing in part from the rachis, and 

 which seldom meet the border at a right angle. 



Throughout the Appalachian trough the typical X. Smithsii has 

 hitherto been found to occur in later beds than the typical X. Poca- 

 hontas. The former is, in the central and southern Appalachian dis- 

 tricts, fairly characteristic of the next higher divisions of the Pottsville 

 series, the Clark and Quinnimont formations, or the Horsepen group. 



The Xeurojyterls ScKiehani Stur is with little difficulty distinguished 

 by its narrower pinnules, which are constricted at the base, the midrib 

 well developed, the nervation strongl}^ curved and meeting the margin 

 at nearly a right angle. The form described by. Stur as X. Dluhoschi^ 

 which Zeiller regards as inseparable from the preceding species, has 

 much that is suggestive of the largest phase of the X. Elrodi of 

 Lesquereux. 



Among the several modifications or variations of X. Pocahontas 

 found in different regions of the Appalachian trough two fairly well- 

 marked forms are present in the Lykens coal region of the Southern 

 Anthracite field. One of these is so difi'erent from the ordinary t3'pe 

 as perhaps to entitle it to more than a varietal distinction. But since 

 its shape and mode of develophient are so similar to the normal type, 

 since its earlier examples are somewhat intermediate, and because it is 

 often difficult to discriminate between small fragments of the latter 

 and material apparently derived from young fronds or apical portions 

 of primary j)innte of the normal form, it seems most practicable to 

 give it only formal or varietal rank. It may be termed and i-harac- 

 terized as follows: 



Neikoiteris Pocahontas var. iN.F.QtAi.is n. var. 



PI. XCLXXXVIII, Fi- r>: I'l. CXC, Fig. 7; PI. CXCl. Fi-rs. 1-4. 



Ultimate pinnte and i)iiHuiI('s nuich larger than those of tiie normal 

 form, often twice as large, somewhat lax, rareh' opposite, the pinnules 



1 A new Tseninpteroid fern and it.s allie.«: Bull. Geol. Soc. America, Vol. IV, 189.3, \>\-i. 119-132, {>!. i. 



