FOSSIL PLANTS. 419 



other like parasitic plants, the whole by compression being crushed, forming 

 a kind of flattened ball. In all these varied appearances of the same plant, 

 no distinct trace of a true nervation can be seen. The lines marked on the 

 figures, exactly as they are perceivable on the stone, are more or less inflated 

 in places, and can be considered, as well as the borders of the filaments, as 

 true veins. They do not branch, and are mostly -parallel. They may, never- 

 theless, represent the parallel groups of vessels which characterize the species 

 of this section of Hymenophyllites. The substance of these plants was evidently 

 soft, for the specimen fig. 6 represents a compound of many of these leaves ap- 

 pressed and crushed together, and the impression is merely of a thin surface. 



All the specimens figured here have been found in concretions at Mazon 

 creek, and nothing except Schizopteris anomald, Brgt., is comparable to this 

 kind of vegetation. 



GENUS PACHYPTERIS, Brgt. 



'Frond simply pinnate or bipinnately divided, bearing upon the same hori- 

 zontal plan, opposite entire coreaceous pinnules, with a medial nerve, or with- 

 out any trace of nervation, narrowed towards the base, not joined to the rachis^ 

 The peculiar disposition of the lobes or leaflets of these plants, is similar to that 

 of the pinnules of some ferns. The genus was established by the celebrated 

 author for two species of the Oolite of England. 



PACHYPTERIS GRACILLIMA, Sp. nov. 



PI. xix, fig. 6 to 8. 



THE specimen represents only simple branches or simple pin- 

 nae, bearing on each side, but on the same plan, opposite very 

 oblique, linear, oblong, obtuse, narrow leaflets, joined by their 

 base to the enlarged border of the rachis, or of a medial nerve, 

 and thus appearing decurrent upon it. The substance of the 

 leaflets is thick, coriaceous, without any trace of a medial nerve. 

 Fig. 6 shows, apparently, a peculiar kind of ramification by 

 innovation. 



The specimen from which the figures and descriptions are made, is on a 

 large piece of shale whose surface is covered by a quantity of simple branches 



