. Fossil plants : for students of botany and geology . Paleobotany. 322 TRIGONOCARPALES [CH. in transverse section, each angle being prolonged as a narrow flange. In one of the sections figured by Brongniart (fig. 495, E) the ribs are not fissured: this is said to be a feature distinguishing Hexapterospermum from Ptychotesta, but the occurrence of a fissured rib in another section suggests that in the structure of. B^G. 495. A, Polypteroapermum BenauUii. B, Ptychotesta tenuis. C, D, Poly lophospermum stephanense; sa, sarcotesta; s, spaces; v, vascular bundles. E, Hexapterospermum stenopterum.
. Fossil plants : for students of botany and geology . Paleobotany. 322 TRIGONOCARPALES [CH. in transverse section, each angle being prolonged as a narrow flange. In one of the sections figured by Brongniart (fig. 495, E) the ribs are not fissured: this is said to be a feature distinguishing Hexapterospermum from Ptychotesta, but the occurrence of a fissured rib in another section suggests that in the structure of. B^G. 495. A, Polypteroapermum BenauUii. B, Ptychotesta tenuis. C, D, Poly lophospermum stephanense; sa, sarcotesta; s, spaces; v, vascular bundles. E, Hexapterospermum stenopterum. F, Diplotesta avellana. G, Taxospermum Griineri. H, Diplotesta Orand'Buryana. (After Brongniart; C, after Oliver.) the ribs there is no essential difference between the two genera. In Ptychotesta pachypterum the testa is prolonged at the chalazal end as in Polylophospermum, and it is possible that there is no generic difference. Wilhamson described a cast from the Coal Measures of Lancashire as Hexapterospermum [= Hexagonocarpus] Noegerraihi'^ (fig. 506, H), but in the absence of anatomical characters it is preferable to avoid the use of Brongniart's term and to assign them to Renault's genus Hexagonocarpus^. Similarly 1 Williamson (77) B. p. 253. ^ gee page Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Seward, A. C. (Albert Charles), 1863-1941. Cambridge : University Press
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