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 Lomarise 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. 
Alethopteeis SOLIDA, Sp, HOY. 
PI. 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 sori and of its leaves, our species is a Polypodium. It 
resembles by these characters the species published by Prof. Brongniart, under 
the name of PJdebopteris 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 g 
observable on the specimen, which is in a concretion from Mazon creek. Our 
species is also related to Polypodites deg an s and Polypodites Lindleyi of Gop- 
pert. 
