FRUCTIFICATIONS FROM THE MAZON CREEK FLORA 17 



are radially trilete, circular in transverse plane, of medium (about 40 to 80 |xm) 

 size and thickness, and ornamented with papillate to conate or small verrucose 

 projections. 



Genus ASTEROTHECA Presl, 1845 



Five specimens of Asterotheca -like fructifications were selected for this 

 study because they show the same type of spore preservation as other fertile 

 specimens studied in this paper. All investigated specimens are preserved in 

 ironstone nodules from the Mazon Creek area. Macroscopic descriptions are 

 given in table 3. The spores are discussed in the following text. Specimens 

 tentatively identified as Scolecopteris are described in the next section. 



Asterotheca (ex Pecopteris) sp. 1 and sp. 2 

 pi. 8, figs. 1-7 



Description.— The spores of Asterotheca (ex Pecopteris) sp. 1 (PP 15338) 

 and sp. 2 (USNM 14212) are monolete, bilaterally symmetrical, and elliptical 

 to bean-shaped in transverse plane. The laesurae are distinct, straight, commonly 

 open, and one-half to two-thirds the length of the long axis; the labra are 1 ^m or 

 less on either side of the commissure. The exine is covered with grana 1 |±mor less 

 in diameter, which are barely visible at the spore margin. The spore wall is 

 less than 1 |im thick. Spore diameters from PP 15338 (30 specimens) show a maxi- 

 mum of 21.8 x 14.0 |Jim, a mean of 18.2 x 12.4 ^m, and a minimum of 15.6 x 9.4 

 [xm. Spore diameters from USNM 14212 (30 specimens) range from 14.6 x 9.4 |am 

 to 20 x 11.7 (am, with an average of 16.8 x 10.6 (jtm. 



Comparison.— Spores are correlated with Laevigatosporites minutus (Ibra- 

 him) Schopf, Wilson, and Bentall, 1944. In the Illinois Basin Laevigatosporites 

 minutus occurs throughout the Pennsylvanian except in the Caseyville Formation. 

 It is most common in the Spoon and Carbondale Formations. 



Asterotheca (ex Pecopteris) sp. 3 and sp. 4 

 pi. 9, figs. 1-6; pi. 10, figs. 1-4; pi. 11, fig. 4 



Description.— The spores of Asterotheca (ex Pecopteris) sp. 3 (USNM 

 13287) and A. (ex Pecopteris) sp. 4 (C 10797) are radially symmetrical, trilete, 

 and originally spherical. Abundant secondary folds commonly obscure the trilete 

 suture. Laesurae are straight and simple. Two laesurae, which are more distinct 

 than the third, form almost a straight line and each is about three-fourths the 

 length of the radius; the third laesura is perpendicular or almost perpendicular to 

 the other two and up to one-half their length. The exine is indistinctly scabrate 

 to finely granulate. The spore wall is less than 1 \±m thick. Diameters of spores 

 from USNM 13287 (40 specimens) range from 14 to 20|jLm, with an average of 16 (im. 

 Diameters of spores from C 10797 (40 specimens) range from 13 to 18fim,with an 

 average of 15 jim. Except for a slight difference in size, the only other difference 

 between the spores of the two species is that the grana on specimen USNM 13287 

 are more closely spaced. 



