FERNS— MEGALOPTERIDEiE—ALETHOPTERIS. 115 



striate below, passing, stroug, to near the apex of the pinnule, where it 

 abruptly terminates. The nerves, more of which spring from the rachis 

 than is indicated in the figure in the Coal Flora, are often obscure on the 

 upper surface, but distinct beneath, generally arching slightly, and forking 

 at or near the base, quite rarely forking above the middle. A large pro- 

 portion of the nerves are simple, and all of them are nearly straight for the 

 greater portion of their length, usually meeting the margin at nearly a 

 right angle and numbering about 30 per centimeter. 



The pinnules of all the specimens are somewhat variable in form, espe- 

 cially the basal pair, conspicuous for their irregularity in length, generally 

 arching backward a little, the lowest ones on the pinna sometimes slightl}' 

 narrowed at the base, but always connected by a narrow lamina. Usually 

 they are near together but not touching, the distance between them being 

 about 1 mm., the borders nearly parallel, the apices obtusely rounded. 



When first studying this species I was impressed by the differences in 

 the pinnules, midribs, and nervation between figs. 2 and 3 (3a), of pi. 

 xxxi of the Coal Flora on the one hand, and fig. 1 of the same plate on 

 the other hand, the nervation of the former in particular being much closer, 

 more oblique, the nervils often forking a second time, thus constituting con- 

 ditions somewhat contradictory to the relations usually existing between the 

 mature and immature specimens. On subsequent examination of the types 

 of figs. 2 and 3, one of them loaned by Dr. Britts, the others having passed 

 with the Lacoe collection into the National Museiim, I found that in the 

 division of the pinna?, in the development of the pinnules, and in nervation 

 these types were Pecopterid — the specimens belonging in fact to Pecopteris. 

 The nervils of the latter, all of which spring from the midrib, are ^'erv 

 oblique at their origin, close and ai-ching obliquely to the border, all of 

 them forking once, the uppei' division forking again before reaching tlie 

 border, where they are fully as much closer than those of the real Aldliop- 

 teris amhigua as they appear in a comparison of figs, la and Set of the plate 

 in the Coal Flora. The midribs of fig. 3 of this plate are found to have 

 been somewhat exaggerated by the draftsman botli as to size and as to 

 abruptness of termination. 



There are, however, in the collections a number of specimens showing 

 the pinnatifid division of the true species, and these, as is seen in Fig. 3, 

 PL XXXVII, or Fig. 9, PL XLI, present the same distinctive characters 



