XXVIl] THINNFELDIA 537 



of the frond as a whole. In the case of branches higher on the 

 rachis the dichotomy becomes unequal and the forked axis is 

 gradually replaced by a simple pinna (fig. 354, A). For this type 

 of frond, Potoni^ proposed the generic name Palviatopteris in 

 place of Diplotmema, which he discards. The long compara- 

 tively slender rachis of P. furcata suggests comparison with 

 the liane species of Lygodium^. 



Cephalotheca. 



This genus was proposed by Nathorst^ for some peculiar 

 bipinnate fertile fronds from the Upper Devonian rocks of 

 Bear Island. The pinnae bear slender forked ultimate seg- 

 ments represented by a few detached fragments (fig. 355, B), 

 associated with the rachises. The fertile pinnae are given off 

 in opposite pairs from the main axis over which they are 

 concrescent (fig. 355, A). A mop-like cluster of sporangia is 

 borne on the lower surface and close to the base of a fertile 

 pinna : the exannulate sporangia are compared with those of 

 Scolecopteris. Nathorst compares Cephalotheca with a Belgian 

 species of Upper Devonian age described by Crdpin' as 

 Rhacophyton condrusorum and by Gilkinet^ as Sphenopteris 

 condrusorum. A similar fossil is also described by Baily " as 

 Filicites Uneatus from the Kitorkan Grits of Ireland. 



The position of Cephalotheca cannot be definitely determined 

 from the available data, but it is more probable that it was 

 a seed-bearing Pteridosperm and not a true fern. Zeiller" 

 has recently expressed the same opinion. 



Thinnfeldia. 



The genus Thinnfeldia, founded by Ettingshausen in 1852 ' 

 on some Hungarian Liassic specimens, though frequently in- 

 cluded in the Filicales, cannot be said to occupy that position 

 by virtue of any well-authenticated filicinean features. It is by 



1 Potoni^ (92). = Nathorst (02) p. 15. 



3 Cr^pin (75). Previously described by Cr^pin (74) as Psilophyton. 



4 Gilkinet (75). » Nathorst (02). 



6 Zeiller (09") p. 20. ^ Ettingshausen (52). 



