FEEIs^S— SPHENOPTEEIDE.E— SPHENOPTEEIS. 59 



thin, smooth, shghtly arched; nervation moderately clear; nerves narrow, 

 straight or nearly straight, somewhat rigid, slightly depressed or obscm'e 

 on the upper surface, distinct and somewhat in relief on the back; primary 

 nerve emitted at an angle of about 45°, very rarely decurrent at the base, 

 and giving off simple branches at an angle of nearly 40°, one nervil to pass 

 into each lobe or crenulation, the dentate pinnules having but one simple, 

 slightly upward turning, rigid nerve to enter each of the few teeth, the 

 younger pinnules having a single nervil, which gives off a branch for each 

 incipient crenulation or developing lobe ; fructiiication unknown. 



The smaller type, illustrated in the Fourth Illinois Report^ as Alethop- 

 teris hymenophylloides Lx., and in the Coal Flora" as Pseudopecopteris hynieno- 

 phyllokles Lx., is represented in the Missouri collections by several speci- 

 mens, two of which are shown in PI. XIX, Fig, 4, and PI. XLIV, Fig. 1. 

 The latter, which shows a section from the upper part of a compound pinna, 

 is comparable to fig. 3 of the plate in the Coal Flora, while the former, 

 which includes the apex of a slender pinna similar to the upper part of the 

 same type, agrees precisely with a specimen (No. 3984 of the I.acoe 

 collection) from Mazon Creek, the type locality, identified under the above 

 name by Professor Lesquereux. Other fragments agree with the details 

 and lower portions of Lesquereux's fig. 3, and leave, in fact, no doubt as to 

 the identity of our plant with the small original type of Pseudopecopteris 

 liymenophylloides Lx. 



The more salient characteristics in the examples from both States are 

 the tlu-ead-like, wide-bordered axis in the rachises, from which the ^itrands 

 turn off to the subordinate pinnae, the rather smooth, oblique pinnee pro- 

 vided with relatively few pinnules, the small pinnules or connate lobes 

 generally very oblique and distant, and the simplicity and apparent rigidity 

 of the nervation, the nervils being regular in the angle of their divergence 

 and seldom forking in the piimule or lobe or small pinnule until a tooth is 

 in process of formation. The usual form of the pinnule is seen in the 

 larger fragment, PI. XLIV, Fig. 1. It is especially difficult to distinguish 

 the pinnules from pinnae, Qwing to the early passage to a pinnatitid arrange- 

 ment in the lower portion of the pinnules. The formation of the first tooth 

 on the lobe, or of the first lobe on the pinnule, whichever term is applied 



' 1870, p. 393, pi. X, figs. 2, 3, 4. 



-Atlas, p. 10, pi. Ivi, figs. 3, 3n-6, copied (rom Kept. Geol. Surv. Illinois, vol. i 



