398 PALEONTOLOGY OP ILLINOIS. 



ALETHOPTERIS LANCEOLATA, Sp. nov. 



PI. xiii, fig. 1 to 3. 



THE specimens represent two parts of simple pinnae or of 

 fronds, with alternate linear lanceolate obtusely pointed leaf- 

 lets, oblique on the rachis, or slightly scythe-shaped, narrowed 

 at the base to half their width, and rounded to the point of 

 attachment to the rachis ; entire on the borders and smooth 

 on the surface. Main or medial nerve half round, moderately 

 thick ; secondary veins attached to it in a very acute angle, 

 alternately branching from the base in veinlets curved in- 

 wardly, as marked fig. 2, the upper ones ascending to the bor- 

 ders of the leaflets, the lower ones becoming confluent in as- 

 cending. 



Of the two specimens which have been seen of this species, and which are 

 figured here, that of fig. 1 seems to represent the upper part of a frond, while 

 the other, fig. 3, looks like the terminal part of a pinna, and therefore the spe- 

 cies is apparently bi or tripinnate. The nervation resembles that of the fol- 

 lowing species, but the veins and their divisions are more oblique, more slen- 

 der and of a more delicate texture. 



Mazon creek; in concretions. 



ALETHOPTERIS EMARGINATA, Gopp. 



Syst. foss., p. 274, PL xvi, fig. 1 and 2. 

 PI. xiii, fig. 4. 



We have in the concretions of Mazon creek many separate leaflets of the 

 same form and of the same size as the one figured. The borders of these linear 

 obtuse leaflets are slightly and equally undulate-lobed, as formed of pinnules 

 connate to the top ; the nervation is nearly similar to that of the former spe- 

 cies, the secondary veins being only more open to the medial nerve, or nearly 

 perpendicular to it, while their branches, generally more marked and thicker, 



