392 PALAEONTOLOGY OP ILLINOIS. 



dendiculartothe rachis, or longer broader linear obtuse regularly 

 undulate, lobed on the borders, and more or less distinct and 

 distant to the base. Medial nerve thin, but deeply marked; 

 veins of the simple pinnules rather curved upwards, forking 

 once only at the middle ; in the undulated lobed leaflets, one 

 of the veins ascends to the sinus, and is twice forked upwards. 



The divisions of the frond of this species appear to have been opposite to 

 each other, and distant, at least in the upper part of the frond, as it is seen 

 fig. 7, representing a specimen which at first seems to belong to another spe- 

 cies. As the nervation, the broad deeply grooved rachis, and the form of the 

 pinnules are the same, it is evident that it merely represents the upper part of'a 

 frond or of a pinna, whose ramification is either in the whole, as in the Glei- 

 chenia of our time, truly dichotomous, or pinnate and dichotomous, as in some 

 of our species of Pteris. The fructifications of this species as represented pi. 

 xiii, fig. 5 and 6, would rather refer it to the genus Gleichenia or even foly- 

 pocfium, than to Pteris. They appear like round, oval, enlarged sori, placed 

 along the borders on both sides of the leaflets, between the branches of the 

 veins, as seen fig. 6 enlarged. The outline only f the fructifications is ob- 

 servable through the substance of the leaflets in the form of an oval ring, de- 

 pressed in the middle, indicating perhaps the point of attachment of an/indu- 

 sium. 



This fine species has as yet been found only in the concretions of Mazon 

 creek, where it is tolerably abundant. 



ALETHOPTERIS CRENULATA, Brgt. 



(Fruiting) PI. xiii, fig. 14 and 15. 



Though the nervation of this fragment is scarcely well enough preserved to 

 permit the ascertaining of its disposition, it is evident, from the form of 

 the pinna and of the leaflets, that it represents a fruiting branch of this spe- 

 cies. The leaflets united at the base, regularly crenulate around, with the bor- 

 ders apparently reflexed, are marked near the margin by two rows of scars of 

 round sori, each placed in a curve of the crenulation, as seen fig. 15 enlarged. 

 The medial nerve, like the veins, are obsolete, and the details of the nervation 

 could be somewhat distinctly observed only on one of the leaflets. In com- 

 paring our figures with that of the sterile parts, published vol. ii of this Re- 

 port, pi. 39, fig. 3, the essential characters are seen to be the same. This spe- 



