Callipteridium.
The name Callipteridium, created by Weiss[1505] as a sub-genus of Odontopteris, is applied by Zeiller and other authors to a few Upper Carboniferous and Permian species characterised by the occurrence of simply pinnate pinnae on the main rachis between the bipinnate primary pinnae. Single pinnules are borne directly on the rachis of the primary pinnae between the pinnate branches. The form and venation of a typical pinnule are shown in [fig. 366], B. Callipteridium pteridium, originally recorded by Schlotheim as Filicites pteridius[1506], has been fully described by Renault and Zeiller from unusually large specimens found in the Commentry Coal-field[1507]. This species illustrates the peculiar morphological features of the genus. The main rachis of the tripinnate fronds, several metres long, shows a combination of dichotomous and pinnate branching; from the zigzag and forked axis are given off bipinnate pinnae and, between these, shorter pinnate branches. The pinnules closely resemble those of Callipteris conferta but reach a greater length; the pinnules borne on the rachises of the lateral branches differ from the others in their broader base and more triangular lamina.
No fertile specimens have been found. It is probable that Callipteridium was not a true fern, and that White[1508] is correct in including it among the Pteridosperms.