548 PTERIDOSPERMS, ETC. [CH. 



name Ptilozamites should perhaps be retained for such long 

 and narrow fronds as that shown in fig. 361 : no species 

 included in Thinnfeldia is known in which the rachis reached 

 so great a length without branching. The habit of Ptiloza- 

 mites Heeri predisposes one in favour of Nathorst's opinion 

 that the fronds are Cycadean : we have no information in regard 

 to the nature of the reproductive organs. 



Ctenopteris. 



This name was instituted by Saporta^ at Brongniart's 

 suggestion, for Liassic species characterised by pinnules like 

 those of Thinnfeldia, but distinguished by the bipinnate habit 

 of the frond. Saporta compares the genus with the Palaeozoic 

 leaves known as Odontopteris, and with Italian Jurassic plants 

 referred by Zigno to his genus Dichopteris. 



The name Gtenozamites is applied by Nathorst^ to the type 

 of frond which Saporta, Zeiller, and other authors refer to 

 Ctenopteris. Nathorst instituted Gtenozamites for fossils agree- 

 ing in the form and venation of the pinnules with his genus 

 Ptilizamites but differing in being bipinnate and not pinnate. 



Fronds of Ctenopteris are characteristic of the Jurassic and 

 Rhaetic series; they are known only in the sterile condition. 

 As Zeiller^ says, Ctenopteris may be a member of the Cycado- 

 filices, an extinct group founded on Palaeozoic plants com- 

 bining Cycadean and Filicinean characters, and some of which 

 are now known to be Pteridosperms. It is probable that the 

 genus is not a true fern: it is more likely to be a member 

 of the Cycadophyta or of some generalised extinct group. 



Ctenopteris cycadea (Brongniart). Fig. 362. 



1828. Filidtes cycadea, Brongniart, Hist. V^g. foss. p. 387, PI. cxxix. 

 1832. Odontopteris cycadea, Berger, Verstein. Coburg Geg. p. 23, 



PI. III. 

 1873. Ctenopteris cycadea, Saporta, Pal. Fran§. Vol. i. p. 355 



Pis. XL. XLI. 



1 Saporta (73) A. p. 352. == Nathorst (78) p. 122. a Zeiller (08) p. 52. 



