CONCLUSION 



37 



vation in this time interval. 



During Pennsylvanian time these ly- 

 copod alliances apparently were dis- 

 tinct. It appears from the present study 

 that Pennsylvanian fossils of lepidoden- 

 drid alliance need not be confused with 

 sigillarian types in phyletic considera- 

 tion. If a precise evolutionary sequence 

 of sigillarian fossils (or any others for 

 that matter) can be established in detail 

 these fossils will become much more 

 useful as stratigraphic indices, and fur- 

 ther investigation along this line is con- 

 templated. 



Aphanozonate megaspores seem defin- 

 itely linked with the sigillarians. In a 

 general way it seems that apiculate 

 species of Aphanozonati represent char- 

 acteristic sigillarians in the Lower 

 Pennsylvanian rocks, whereas levigate 

 Aphanozonati are more abundant in the 

 Upper Pennsylvanian. Detailed studies 

 of these species based on isolated spores 

 and spores associated with sigillarian 



cones should help in further indicating 

 the sigillarian evolutionary sequence as 

 well as in serving directly stratigraphic 

 purposes. As these spores are obtain- 

 able from coal, they also will aid in 

 evaluating the importance of sigillarians 

 in coal formation. Thus, the greater 

 abundance of the aphanozonate species 

 Trileies reinschi and Triletes hrevispicu- 

 lus in the Herrin (No. 6) coal (Schopf, 

 1938, pp. 27, 29) in the coal bench im- 

 mediately overlying the blue-band clay 

 parting is one of the factors to be con- 

 sidered in explaining the origin of this 

 tj^pe of coal. Furthermore the im- 

 portance of the sigillarians as plants 

 capable of establishing themselves on 

 what must have been a dense clay sub- 

 stratum (the blue-band) must be recog- 

 nized. These aphanozonate spores are 

 by no means alone in this portion of the 

 coal bed but, in marked contrast to 

 some of the other species present, they 

 are definitely more abundant there. 



