PENNSYLVANIA TREE FERN COMPRESSIONS 



Artisophyton mclayi (Lesquereux, 1866) comb. nov. 

 Text fig. 3, D; pi. 4; pi. 6, fig. 1 



Basionym : Megaphytum McLayi Lesquereux, L., 1866, Report on 

 the fossil plants of Illinois, pi. 48, p. 458; in: Worthen, A. H. , 1866, 

 Palaeontology: Geological Survey of Illinois, v. 2. 



Holotype : ISM 1782 



Specimens : ISGS PB-1298, ISM 1619, PP 726, PP 2259 



Occurrences : Energy Shale Member (shale above Herrin (No. 6) 

 Coal Member), Carbondale Formation; Francis Creek Shale Member (shale 

 above Colchester (No. 2) Coal Member), Carbondale Formation; ? shale 

 above Murphy sboro Coal Member, Spoon Formation. 



Discussion 



Artisophyton approximatum has been chosen as the type species 

 because it is the first published species having the configuration 

 of the vascular bundle as described in the diagnosis of the genus. 



In Illinois only two species of this genus have been reported, 

 A. mclayi and A, insignis. The two species differ in the height to 

 width ratios of their leaf scars (tables 1 and 2; text fig. 5). The 

 scars of A. mclayi are wider than they are high, while those of A. in- 

 signis are higher than wide. Both species were 20 cm or more in 

 diameter. 



Artisophyton mclayi was considered a synonym of A. approximatum 

 by Janssen (1940, p. 74), who used height to width ratio as a character- 

 istic. A. approximatum (Lindley and Hutton, 1834), A. goldenbergii 

 (Weiss, 1860), and A. mclayi (Lesquereux, 1866) are very similar in 

 height to width ratio. However, Crookall (1955, p. 75) pointed out that 

 there are differences in shape and in size. The scars of A. approximatum 

 apparently do not touch each other, and they are less angular than those 



TABLE 1 - MEASUREMENTS OF SPECIMENS OF ARTISOPHYTON INSIGNIS 

 FROM ILLINOIS (H:W = height to width ratio) 



Leaf scar 



Outer 



vascular 



bundle 



Height 



Width 



H:W 



Height 



Width 



H:W 



(mm) 



(mm) 





(mm) 



(mm) 





150 



110 



1.36 



92 



80 



1.14 



140 



110 



1.27 



90 



68 



1.32 



135 



110 



1.22 



83 



78 



1.06 



130 



100 



1.30 



80 



74 



1.08 



125 



90 



1.39 



80 



65 



1.23 



- 



- 



- 



60 



55 



1.09 



68 



57 



1.19 



50 



40 



1.25 



90 



78 



1.15 



60 



55 



1.09 



