2k ILLINOIS STATE GEOLOGICAL SURVEY CIRCULAR 500 



1888 Megalopteris dawsoni, Dawson, p. 76, fig. 26 



191^ Megalopteris dawsoni, Stopes, p. 53-55, pi. 13, 

 fig. 3*+ (first photograph) 



Arnold (193*0 and Wood (1963) also figured specimens that can 

 probably be attributed to M. dawsoni . 



Description . — The pinnules are strap shaped and have an acute 

 tip. The margin is entirely or slightly undulate. The pinnules are 

 more than 70 mm long (as long as 150 mm according to estimates) and at 

 least 20 mm wide. The pinnules become unequal sided at the base, with 

 a width of only 7 to 12 mm. The angle of attachment of the pinnules 

 ranges from 16° to 46°. The midrib is strong and 1 to 2 mm wide. The 

 lateral veins fork two or three times. There are 21 to 30 veins per cm 

 on the margin, with an average of about 23. The lateral veins are curved 

 in the first half of their course and beyond that continue straight to 

 the margin. They form an angle of 12° to 20° with the midvein, of 35° 

 to h5° in the middle, and of 75° to 85° (90° in one case) with the margin, 



The measurements are based on seven specimens. The variation is 

 certainly higher than indicated here and must be taken into account in 

 establishing a synonymy. 



Megalopteris ovata Andrews 

 Text fig. 8B, E; pi. 7; pi. 6, fig. k 



Synonymy 



1875 Megalopteris ovata Andrews, p. *+17 9 pi. *+7, 

 figs. 1, 2 



iQQk Megalopteris dentata Lesquereux, p. 833 (no figure) 



Description . — The pinnules are lanceolate and have an acute tip. 

 The margin is entire to slightly crenulate. The pinnules are 30 to 70 

 mm long and 7 to 13 mm wide. They are unequal sided at the base and 

 only k to 7 mm wide. The angle of attachment of the pinnules ranges 

 from 18 ° to 52°. The midvein is distinct and O.k to 0.7 mm wide. The 

 veins fork one to three times in many specimens, but are not clearly 

 visible. Round bodies occur in the laminae between the veins. They are 

 probably glands and are not always preserved. There are ik to 23 veins 

 per cm on the margin. The lateral veins are curved and form angles of 

 10° to 15° with the midvein, k^° in the middle, and k0° to 60° with the 

 margin. 



Discussion . — M. dentata was never figured but Lesquereux (188U) 

 gave a relatively detailed description. The specimens (no. 783 of the 

 Lacoe Collection) mentioned by Lesquereux in the original description 

 are now in the collection of the Field Museum of Natural History in Chi- 

 cago. They fit well the description of M. ovata given by Andrews (1875). 



