This generic title I propose to restrict to petrified seeds exhibiting the characters described by Brongniart[939] and more recently by Bertrand[940] in _C. sclerotesta_ and _C. drupaceus_. In general organisation seeds of this generic type agree with those of recent Cycads and with the seed of _Ginkgo biloba_, but there are certain distinguishing features. An important character is afforded by the course and place of origin of the lower vascular strands from the main supply at the base of the seed. The outer vascular system consists of two bundles given off from the main strand, before it reaches the sclerotesta, which pass up the sarcotesta (fig. 500, B). In _Rhabdospermum_, on the other hand, the corresponding bundles arise at a higher level and form recurrent strands which penetrate the sclerotesta before passing up the fleshy part of the integument (cf. fig. 501, E). [Illustration: Fig. 500. _Cardiocarpus drupaceus_ var. _expansus_. A, transverse section of the testa approximately in the middle of the seed; _v_, vascular bundles. B, diagrammatic sketch, adapted from Brongniart’s drawing of the base of the seed showing the sarcotesta, _sa_, the sclerotesta, _sc_, and the pad of vascular tissue, _d_, at the base of the nucellus. (After Brongniart.)] _Cardiocarpus sclerotesta_ Brongniart. The testa is differentiated into an inner shell and an outer sarcotesta (fig. 501, A; the sclerotesta is shown in black); there is a well developed pollen-chamber (_pc_) and below this the prothallus-tissue is prolonged as a blunt and short tent-pole, _b_, as in _Gingko_ and in several fossil seeds. On each side of the apical tent-pole the slightly shrunken prothallus shows two small archegonia, _a_, which in the relatively small size and spherical form of the egg-cells resemble those of _Ginkgo_. In transverse section (fig. 501, B) the seed is bi-convex and at each end of the major axis the sclerotesta forms a small keel. There are two sets of vascular bundles concerned in the supply of material to the ovule; a lower pair of bundles given off from the central strand in the sarcotesta (fig. 500, B) which pass to the apical region in the inner tissues of the sarcotesta in the principal plane (fig. 500, A, _v_), and an inner set of bundles that pass up the peripheral tissue of the nucellus. The species described by Brongniart as _Cardiocarpus (Cyclocarpus) tenuis_ and _C. nummularis_ have been removed by Bertrand[941] from _Cardiocarpus_ on the ground that the integumental bundles pursue a course like that in _Rhabdospermum_; it is now referred to the new genus _Cyclospermum_[942].