AERANGEMENT OF PLANTS OF THE COAL. 



197 



The student will find it necessary to devote particular 

 attention to the fossil ferns, to enable him to discriminate 

 the different genera and species. The four genera which 

 most nearly resemble each other are neuropteris, sphenopteris, 

 pecopteris, and odontopteris.* The following may be mentioned 

 as distinctive characters. Neuropteris is known from spheno- 

 pteris by its leaves being cordate at the base, while this cha- 

 racter is reversed in sphenopteris, in which, near the base, 

 the leaves are usually smallest ; the shape of the leaflets is 

 moreover different, those of sphenopteris being lobed, while 

 those of neuropteris are not. Pecopteris, again, is distin- 

 guished from neuropteris by its leaves being occasionally tri- 

 pinnate, which is never the case with neuropteris ; the mid- 

 rib of pecopteris also runs quite through the leaflet, while in 

 neuropteris it vanishes at the apex : the veins, moreover, of 

 pecopteris run almost perpendicular to the mid-rib ; while in 

 neuropteris they are oblique and curved; and the genera 

 odontopteris and neuropteris are distinguished from each 

 other by the veins of the former proceeding into the segments 

 directly from their base, without collecting into a distinct 

 mid-rib, and by those of the latter gradually diverging from 

 the mid-rib, as they approach the point of the segments. 



We subjoin a magnified leaf of a common species of each 

 genus ; and for farther particulars, such as the form, mark- 



FIG. 133. 1. Neuropteris. 2. Sphenopteris. 3. Pecopteris. 4. Odontopteris. 



ings, and other characters of recent leaves and stems, analo- 

 gous to those of fossil specimens, we again refer our readers 



* Pict. Atlas ol. iv. 



