196 Sellards—F7'onds of Crossoiheca and Myriotheca. 



tion of the spores of some Carboniferous ferns, it is pointed 

 out that, as far as the radiating lines (" lines of dehiscence ") 

 at the apex are concerned, they cannot be considered character- 

 istic of megaspores. 



The fructification of several genera of Carboniferous ferns 

 is well shown in an exceptionally large and complete collec- 

 tion from Mazon Creek, Illinois, in the Yale Museum. The 

 sporangia are often preserved, and in many cases the spores 

 are found in place, and can be removed and studied. * In the 

 present paper the Mazon Creek representatives of two inter- 

 esting genera, Crossotheca and Myriotheca^ will be described, 

 together with the spores of some other species. 



In the earlier American literature many of the fertile ferns 

 were grouped together without sufficient regard to their true 

 generic separation. Sorocladus^ as established by Lesquereux,* 

 was so broadly defined as to include more than one natural 

 ^enus. S. stellatus was the first of the five species described 

 under the genus. Four of the species referred in the " Coal 

 Flora " to Sorocladus had been previously placed by Les- 

 quereux in the Tertiary Staphylopteris Presl. It was probably 

 Schimper's objection to considering these forms under Presl' s 

 genus that led Lesquereux to create a separate genus for them.f 



One of the five original species of Soi'ocladus^ S. ophioglos- 

 soides^ has been referred by David White to Crossotheca, and 

 S. sagittatiis was recognized as falling naturally within the same 

 genus.:}: 



Crossotheca. 



Zeiller, Ann. Sci. Nat. (Bot.), ser. 6, vol. xvi, 1883. 

 Crossotheca is a genus of more than ordinary interest, because 

 of its dimorphic fronds, its large marginal sporangia, and large 

 spores. Several species are known in Europe, all of Coal 

 Measure and Permian age. Besides the two species just men- 

 tioned from this country, a third is added in the present paper. 



Crossotheca sagittata. 

 Plate VII, figures l-3c, 8. 



Staphylopteris sagittatus Lesq., Geol. Surv. 111., vol. iv, p. 407, pi. xiv, 

 figs. 4-6. 1870. 



Pecopteris abbreviata Brongn. ? Lesq., Geol. Surv. 111., vol.iv,p. 403, 1870; 

 Second Geol. Surv. Penn., Description of the Coal F]ora, vol. 1, p. 248, 

 pi. xlvi, figs. 4-6a, 1880. 



Sorocladus sagittatus Lesq., Coal Flora, vol. i, p. 329, 1880; Atlas, pi. 

 xlviii, figs. 10-106, 1879 ; vol. iii, p. 761, pi. C, figs. 4-5, 1884. 



Pecopteris Fontainei, Lesley's Diet, of the Fossils of Penn., p. 606, 1889 

 text figure. See, also, Lesquereux, unpublished manuscript. 



* Second Geol. Surv. Penn., Description of the Coal Flora, vol. i, p. 327, 

 1880. 



f Paleont. veg^t.. vol. iii, p. 512. 



jiMon. U. S. Geol. Surv., No. 37, Flora of the Lower Coal Measures of 

 Missouri, pp. 60-64, 1899. 



