EARLY PENNSYLVANIA FLORA FROM WEST-CENTRAL ILLINOIS 29 



Description . — Size and shape of pinnules highly varied; depend- 

 ing on the position in the pinna. Pinnules slightly to strongly lobed; 

 general outline diamond- shaped to ovoid; three to seven lobes per pin- 

 nule. At the base, pinnules are decurrent on the proximal side and 

 deeply incised on the distal side; toward the tip of the pinna, pinnules 

 tend to be attached along their entire base. Tips of pinnules obtuse, 

 appearing nearly acute in some specimens. 



Lobes are generally rounded and diamond shaped, and a continual 

 morphogenic development from lobes into pinnules can be observed. The 

 size of pinnules ranges from 5 x 3.7 mm to 12 x 9 mm, with an average of 

 8x7 mm. Pinnules barely touch each other or have space between them. 

 They are attached obliquely and form an angle of 70° to 80° on the acro- 

 scope side and 50° to 60° on the basiscope side. Basal pinnules are 

 sometimes larger in more mature parts of the frond, where they appear 

 somewhat mariopteroid. 



Venation is a mixture of open dichotomous and pinnate. The mid- 

 vein is straight to undulate in the lower two-thirds of the larger pin- 

 nules and is not different from lateral veins in smaller (younger) pin- 

 nules. Only one vein enters larger pinnules, but in lobes and smaller 

 pinnules several veins may enter. In larger pinnules the first distal 

 lateral vein runs parallel to the pinna axis and can thus create the im- 

 pression that the secondary lateral veins coming from it are actually 

 entering the pinnule directly from the pinna axis. Lateral veins are 

 curved outwards. Venation is distinct but not very coarse. 



Between the veins there are numerous round bodies (probably 

 glands) that are distributed over the entire lamina (pi. 11, fig. 2). 

 These glands are visible only in certain kinds of preservation and thus 

 cannot be used as a descriptive characteristic. Construction of frond 

 unknown, but at least three times pinnate. 



Discussion . — Eusphenopteris morrowensis is one of the most com- 

 mon fossils in the Spencer Farm Flora and therefore can be well charac- 

 terized. However, all specimens are fragments, even where they cover 

 entire bedding planes, and it is therefore not possible to reconstruct 

 the frond. It is nevertheless clear from the shape of the pinnules that 

 this species belongs to the genus Eusphenopteris , which was recently re- 

 vised by Amerom (1975). 



Our material is best comparable with Diplothmema morrowensis , 

 which have therefore to be transferred to the genus Eusphenopteris • 

 Amerom (1975 9 p. 62) actually mentions D. morrowensis as closely compar- 

 able to E. aldrichii (D. White) Amerom without proposing the new combina- 

 tion. Thus, Amerom (1975) recognized the proper position of the species, 

 and the formal change is made here with the approval and under the name 

 of Dr. van Amerom. 



Amerom (1975) distinguishes several sections within the genus 

 Eusphenopteris . Our material belongs in the section of E. neuropteroides , 

 The Spencer Farm material is also comparable to Sphenopteris cheathami , 



Text fig. 10 - Fossil plants from the Spencer Farm Flora. A, B, Sphenopteris pres- 

 lesensis . C-G, Rhodeopteridium phillipsii. Bar scales are 5 mm long, except 

 where noted. 



