Scott and Mas leu . — The Structure of Trigonoccirpus. 131 
One difficulty in the interpretation of the specimen shown in PI. XIII, 
Fig. 18, is that the longitudinal ridge apparently extends to the bottom of 
the body of the seed, while, as we have before mentioned in this paper, the 
ordinary internal casts usually show the ridges disappearing towards the 
base of the seed. Examination of a number of specimens, of Carpolithes 
alata and of the ordinary internal casts at the Natural History Museum 
makes it highly probable that in Fig. 18 the real base of the seed is not 
seen. The ridge shown is of exactly the same length as one of the ridges 
of many of the internal casts, and the real base of the seed was in all 
probability unribbed. We feel little doubt as to the specimen shown in 
Fig. 18 being really mainly preserved as an internal cast, with a thin coaly 
layer representing the sclerotesta preserved in places. 
The true interpretation of impressions such as those shown in Figs. 16, 
17, 18, presents considerable difficulty, and becomes possible only after the 
internal structure of the petrified specimens has been worked out in detail. 
References. 
Brongniart (’28) : A. Brongniart. Prodrome d’une histoire des vegetaux fossiles. Paris. 
(’49) : Tableau des genres de vegetaux fossiles (Diet. univ. d’hist. nat., vol. xiii). 
Paris. 
(74) : Ann. des Sci. Nat., Bot., tome xx, pp. 234-65. 
(’81) : Recherches sur les graines fossiles silicifiees. Paris. 
Hooker and Binney (’55) : J. H. Hooker and E. W. Binney, On the structure of certain Lime- 
stone Nodules enclosed in seams of Bituminous Coal, with a description of some Trigono- 
carpons contained in them. Phil. Trans., vol. cxlv. 
KlDSTON (’86) : R. Kidston, Catalogue of the Palaeozoic plants in the Department of Geology and 
Palaeontology. British Museum, London. 
Lang (’00) : Lang, Development of Cycadean Sporangia, II. Ann. Bot., vol. xiv. 
Lindley and Hutton (’31— ’37) : J. Lindley and W. Hutton, The Fossil Flora of Great Britain. 
3 vols. London. 
Oliver (’04) (1) : F. W. Oliver, On the Structure and Affinities of Stephanospermum, Brongn., 
a genus of fossil Gymnosperm seeds. Trans. Linn. Soc. Lond. Botany, vol. vi. 
(’04) (2) : Notes on Trigonoccirpus , Brongn., and Polylophospermum, Brongn., two genera 
of Palaeozoic Seeds. New Phytologist, vol. iii. 
Parkinson (’ll) : J. Parkinson, Organic Remains of a former World. London. 
Renault (’81-’85) : B. Renault, Cours de Botanique Fossile. 
Scott and Maslen (’06) : D. H. Scott and A. J. Maslen, Note on the Structure of Trigono- 
carpan olivaeformy . Ann. Bot., vol. xx. 
Scott (’99) : D. H. Scott, On the Structure and Affinities of Fossil Plants from the Palaeozoic 
Rocks. III. On Medullosa anglica , a new Representative of the Cycadofilices. Phil. 
Trans. Roy. Soc. Series B, vol. cxci. 
- (’05) (1) : What were the Carboniferous Ferns? Jour. Roy. Micro. Soc. 
(’05) (2) : The Early History of Seed*bearing Plants, as recorded in the Carboniferous 
Flora. Wilde Lecture. Memoirs of the Manchester Literary and Philosophical Society, 
vol. xlix, No. 12. 
K 2 
