FOSSIL PLANTS. 397 



lets being scarcely perceivable to the naked eye, this species rather resembles 

 a Cycas than a fern. With a strong glass, the veinlets are seen as marked on 

 fig. 4, enlarged, and these indicate the true relation of the plant. 



The specimen may represent a part of a frond in the process of unfolding 

 its leaves, which appear as being pressed upon each other on the lower side of 

 the rachis, and at the same time, still half uncinnate. It may also be the re- 

 presentative of a species in its full development. Some Lomarix of our time 

 resemble it, by the nervation and the form of the leaflets. It has no relation 

 with species known from the Coal Measures. 



Mazon creek ; -in concretions of clay iron ore. 



ALETHOPTERIS SOLIDA, Sp, nov. 



PL xi, fig. 5-7. 



THIS species is, like the former, known only by a frag- 

 ment of a frond or of a pinna. It is pinnately divided into 

 narrow leaflets, attached to a proportionally very broad flat 

 rachis, by the enlarged base of a thick medial nerve. These 

 pinnules, a little longer than one inch, perpendicular to the 

 main rachis or slightly turned upwards, are linear obtusely 

 pointed, disconnected at the enlarged rounded base, and en- 

 tire. They bear along the borders, at equal distances from 

 each other, round groups of sporanges, apparently divided 

 star-like into five round dots, as marked in fig. 7. 



By the position of its sort and of its leaves, our species is a Polypodium. It 

 resembles by these characters the species published by Prof. Brongniart, under 

 the name of Phlelopteris polypodioides, Veg. foss., p. 372, pi. 83, fig. 1, and if 

 the nervation should prove to be the same, the American species would be dis- 

 tinguishable only by the broad rachis, the enlarged base of the medial nerve, 

 and the separation of the leaflets. No trace of secondary veins or veinlets i s 

 observable on the specimen, which is in a concretion from Mazon creek. Our 

 species is also related to Polypodites clegans and Polypodites Lindleyi of Gop- 

 pert. 



