16 ILLINOIS STATE GEOLOGICAL SURVEY CIRCULAR 500 



The fructification genera of the Noeggerathiales , Noeggerathi- 

 ostrobus Feistmantel, Discinites Feistmantel, and Lacoea Read 19^-6, 

 emend. Leary 1973 , can "be arranged in a form- evolutionary sequence that 

 requires only small transformations between the different forms (text 



fig. 5E). 



The line started possibly with a hypothetical form similar to 

 Archaeopteris . The pinnules of this hypothetical form would form Noeg- 

 gerathiostrobus after the formation of laminae (webbing). A shortening 

 of the axis between the attachment points of the fertile pinnules would 

 yield a fructification of the Lacoea type. Further shortening and fusion 

 of two pinnules would produce the disc-shaped sporangiophore of Discinites, 

 It has to be emphasized that this conclusion is purely hypothetical and 

 indicates only a possible trend. 



Lacoea seriata Read emend. Leary 

 PI. U, figs. 6-8 



Description . — Cone consisting of semicircular sporophylls, which 

 alternate on a rather thick axis. Sporophylls attached close to each 

 other, thus creating a very dense cone. Each sporophyll surface is 

 covered with numerous diamond-shaped sporangial scars arranged in oblique 

 rows forming a distinctive pattern. Margin of each sporophyll bends 

 toward the distal end of the cone and bears a fringed border. Sporophylls 

 often found detached. 



Discussion . — The genus Lacoea was recognized by David White be- 

 fore 1908, but he never described it (White, 1908, p. 269). Read (19^6) 

 described Lacoea, but misinterpreted its morphology and systematic po- 

 sition. The genus was redescribed and reinterpreted by Leary (1973), 

 who recognized that it belongs to the Noeggerathiales. 



Lacoea is in appearance very similar to Discinites. The pattern 

 of sporangial attachment and the fringed margin are identical. The only 

 difference is that Lacoea has semicircular sporophylls whereas Discinites 

 has disc-shaped sporophylls. 



Lacoea has so far been found only in the lower part of the Penn- 

 sylvanian and has been reported or has been found in the following local- 

 ities : 



Dutch Mountain, Pennsylvania (Read, 19^+6) 



Youngs town, Ohio (Read, 19^6) 



Rushville, Ohio (seen in photograph of collection specimen) 



Brown County, Illinois (this report) 



northwestern Illinois (D. White, 1908) 



Rock Island County, Illinois (field observation) 



In at least five of these six locations, Lacoea occurs with 

 Palaeopteridium reussii or a very similar form. Nemejc (l9*+l) reported 

 that Discinites and Palaeopteridium nearly always occur together and 

 concluded that there was at least a good chance that Discinites might be 

 the fructification of Palaeopteridium. It is possible that Lacoea is 

 just another fructification of Pal aeopteridi urn-like foliage. 



