We have no proof as to the nature of the plant which bore seeds of the _Stephanospermum_ type, but it is significant that the specimens occur in close association with fragments of _Alethopteris_ and _Myeloxylon_, a circumstance that favours the view, based on the resemblance of these seeds to _Trigonocarpus_, that _Stephanospermum_ is the seed of a member of the Medulloseae. =Polylophospermum[891].= Brongniart. The type-species _Polylophospermum stephanense_ Brongn.[892], founded on partially preserved material from Grand’ Croix, is a narrow hexagonal seed 15 mm. long. Additional facts as to the structural features have been contributed by Oliver[893]. The testa is differentiated into an inner shell (sclerotesta) and an outer flesh (_sa_, fig. 495, C, D): the sclerotesta has six prominent, fissured, ribs, one at each angle, and between these are six solid and less prominent secondary ribs. Oliver states that there is an outer series of vascular bundles in the sarcotesta, one bundle immediately external to each secondary rib (fig. 495, C, _v_). In the presence of two kinds of ribs and in the relation of ribs to tracheal strands _Polylophospermum_ agrees with _Trigonocarpus Parkinsoni_. Strands of short tracheids supply the peripheral region of the nucellus and, as in _Stephanospermum_, reticulate elements extend as far as the floor of the large pollen-chamber. There was probably no lateral union between nucellus and integument. A striking feature is the prolongation of the testa at each end of the seed to form an open chamber surrounding the micropylar beak and the seed-base (fig. 495, D, _s_, _s_): the apical chamber, though relatively more prominent, is comparable with that in _Stephanospermum_, while the basal chamber recalls that in the seed named by Scott and Maslen _Trigonocarpus Oliveri_[894] but subsequently removed by Salisbury[895] from that genus. There is no evidence as to the parent-plant of _Polylophospermum_, but it may be assumed to have been a Pteridosperm, probably one of the Medulloseae. [Illustration: Fig. 498. A, B, _Codonospermum_. A, _C. olivaeforme_, longitudinal section showing the seed-proper and the air-chamber, _s_; _pc_, pollen-chamber. B, Diagrammatic sketch of a _Codonospermum_ showing the vascular supply, _v_, and the fibrous arcs, _f_, in the wall of the lower part of the seed. C, _Aetheotesta elliptica_, _s_, sarcotesta with lacunae; _v_, vascular supply. (After Renault.)] =Codonospermum[896].= Brongniart.