394 PALEONTOLOGY OF ILLINOIS. 



In considering the form of its fructifications, this species should 

 be separated as the type of a peculiar genus. 

 Mazon creek ; in concretions of clay iron ore. 



ALETHOPTERIS HALLII, Sp. nov. 



PL x, fig. 7 and 8. 



FROND bi-pinnate ; pinna3 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 serrufa, Lesqx., Penna. Geo). 

 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 the same species. 



Mazon creek ; in concretions found by Mr. M. S. Hall. 



ALETHOPTERIS EROSA, Gein. 



Verst., p. 29, PI. 32 r tig. 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 ; thoae especially in 



