FERNS— MEGALOPTERIDE.E—ALETHOPTERIS. 1 19 



Radnitz. A striking- feature is the rarity of small pinnate pinupe of the pro- 

 portions connnou in ^1. Serlii, but very few of sucli small size being- seen, 

 though the collection contains three large slabs representing- segments of 

 primary (1) pinna^ with rachises as wide as IG nun., provided on both sides 

 with these slender secondary pinna? bearing pinnules comparable in dimen- 

 sions to the figure to which reference has just been made, or to those 

 replacing the pinnatifid divisions at the tips of pinnffi of a superior order in 

 the normal form of Alethopteris Serlii. 



Frequently there is no contraction toward the bases of the pinnules, 

 and often, especially in the largest, sometimes exceeding 4 cm. in length and 

 measuring 5 to 7 mm. in width, the borders are folded in under, causing 

 the pinnules to appear to taper to an acute point. Several examples from 

 Missouri labeled Alethopteris loi/cJiitica I have found, by removing the matrix 

 from the border, to belong to the form in question, and these cases, in fact, 

 comprise the only specimens from this region that I can find in any collection 

 to have been referred to the latter species. 



As in other species of Alethopteris, where well preserved, the veins may 

 be seen to spring from a raised threadlike irregular line traversing the 

 center of the canal along the upper surface of the midrib. They are quite 

 coarse, in relief on the rather coriaceous lamina, and pass, moderately 

 straight, to the border In the largest pinnules the midrib also is seen to be 

 punctate, while the nervation becomes rather more distant, counting 28 to 34 

 per centimeter at the margin, its characters remaining otherwise the same. 

 The general aspect of the plant, as seen in Fig. 5, PL XLII, is much like 

 the illustration of A. Serlii, given by Zeiller in tig. 1, pi. xxxvii, of the 

 Valenciennes flora. 



The varietal distinction of this Missouri form, which 1 have thought 

 might be of stratigraphic utility, must be reg-ai'ded as tentative, the question 

 of its survival or elimination depending on the results of further study of 

 material from other portions of the American Carboniferous. However, the 

 phase should at least be illustrated in our American literature. 



The diagnosis of the variety missouriensis is as follows: 



Fronds tripinuate, quadripinuatifid or quadripinnate near the base, very long, 

 spreading; main rachis reaching a width of 45 mm. or more, both it and its divisions 

 rather coarsely striate, and thinly set. esi)ecially on the dorsal surface, with very dis- 

 tinct short spines or spi)ious scales; ]irimary piiin;e very long, open, linear-lanceolate. 



