Sellards — Fronds of Crossotheca and Myriotheca. 195 



Art. XXII. — On the Fertile Fronds of Crossotheca and Myrio- 

 theca, and on the Spores of other Carboniferous Ferns^ 

 from Mazon Creek, Illinois : by E. H. Sellards. (With 

 Plate YII.) 



Information in regard to the spore-bearing organs of Car- 

 boniferous ferns has accumulated slowly and with difficulty. 

 The parts of the plants are usually disconnected, and more or 

 less fragmentary. Dimorphic genera are not uncommon, and 

 specimens connecting the fertile and sterile segments or fronds 

 are rare. It is usually difficult to correlate genera described 

 from microscopic structure with others based on plant impres- 

 sions. And yet, a satisfactory knowledge of a considerable 

 number of genera and species has resulted from the work of 

 the various investigators who have taken up this subject since 

 the time of Brongniart. These investigations indicate that 

 ferns with the annulus absent or but slightly developed, and 

 having other Marattiaceous characters, predominated in the 

 Carboniferous, and included a much greater range of form and 

 structure than is seen in the living representatives of the 

 family. Besides the numerous exannulate ferns, others are 

 known with a well-developed annulus, and are, therefore, pre- 

 sumably Leptosporangiate. The reference of these fossils to 

 their respective families of living ferns is attended with more 

 or less doubt. The Hymenophyllacese, Gleicheniacese, Schizse- 

 acese, and Osmundacese have been recognized with some degree 

 of certainty. 



Prof. Penault, of the Museum of Natural History of Paris, 

 has recently described Par'kerioidea^Qi\2iXx\t, a genus from the 

 Coal Measures of Grand' Croix, near St. Etienne. The char- 

 acter of the annulus, the form of the spores, and the ornamen- 

 tation of the exospore have led him to refer this form to the 

 Parkeriacese. Certain of the spores show sculpturing, while 

 others are smooth and have three radiating lines at the apex. 

 The former are interpreted as microspores, the latter as mega- 

 spores.* 



The same writer had previously detected what he believed 

 to be indications of heterospory in Pecojpteris, one of the 

 Marattiaceous ferns,t as well as in an extinct family of ferns, 

 the Botryopteridese.:}: The evidence of heterospory in the 

 Botryopteridese has not been fully accepted. § The papers on 

 Pecopteris and Parkerioidea are mentioned more fully later 

 in the present article, where, in connection, with the descrip- 



* Comptes Rendus de I'Academie des Sciences, March 10, 1891. 

 flbid., October 21, 1891. X^vXX. Soc. Hist. Nat., Autun., iv, 1891. 



§See Scott, Studies in Fossil Botany, p. 289 ; Zeiller, Elements de Paleo- 

 botanique, p. 74. 



Am. Jour. Sci. — Fourth Series, Yol. XIV", No. 81.— September, 1902. 

 14 



