394 
PALAEONTOLOGY OP ILLINOIS. 
V . . 
Ill considering the form of its fructifications, this species should 
be separated as the type of a peculiar genus. 
JVlazon creek • in concretions of clay iron ore. 
PL x, fig. 7 and 8. 
Frond bi-pinnate j pinnae ‘perpendicular to the straight 
round mainrachis, linear, alternate, narrow, close to each other, 
apparently short, merely cut on the borders by obtuse narrow 
lobes, either emarginate or square at the top, separated by 
short obtuse sinuses. Veins and veinlets deep and narrow, the 
primary ones ascending to the middle of the sinuses and fork¬ 
ing twice upwards as seen in fig. 8 , enlarged. 
This species is closely related to Alethopteris serrula , Lesqx., Penna. Geol. 
Report, p. 865, pi. xii, fig. 1, differing from it by its shorter, broader pinnae, 
placed close to each other; by its more obtuse lobes, and by the primary divi¬ 
sions of the veins, ascending to the middle of the sinuses, and not to the point 
of the lobes. Though in both species the borders of the pinnules are appar¬ 
ently reflexed, these differences are too marked to be considered mere varieties 
of the same species. Nevertheless, it might be possible that the specimens from 
Illinois represent a sterile frond, and those of Pennsylvania fruiting branches 
of thosame species. v 
Mazon creek; in concretions found by Mr. M. S. Hall, 
Alethopteris erosa, Gein, An*-- Jj d 0 ^v. /. 
Verst., p. 29, PI. 32, fig. 7-9. 
Pecopteris erosa, Gutb. (1843.) 
Numerous and large specimens referable to this species have been found by 
Mr. S. S. Strong, in the roof shales of the coal at Morris. 
The American plant merely differs from that of Europe by the longer divi¬ 
sions of the three-pointed lobes, and by the much longer pinnae. The same 
fronds, or parts of fronds, bear sterile and fruiting pinnae ; those especially in 
