398 
PALEONTOLOGY OF ILLINOIS. 
Alethopteris Lanceolata, Sp. noy. 
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, PI. 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, 
