Genera. _Cardiocarpus_; _Cyclospermum_; _Cycadinocarpus_; _Rhabdospermum_; _Mitrospermum_; _Diplotesta_; _Leptocaryon_; _Taxospermum_; _Compsotesta_. These generic names are all used in the following pages for seeds known to possess certain anatomical features; there are also included in the Cardiocarpales the genera _Samaropsis_, _Cordaicarpus_, and _Rhabdocarpus_, but it is proposed to limit their use to specimens which furnish no anatomical data and cannot therefore be assigned with equal confidence to a section of seeds based on definite morphological characters. It is certain that some at least of the seeds described under these names would, if preserved as petrified specimens, be included in one or other of the genera named above. There is ample proof that some of these seeds were borne on Cordaitean plants and that the group as a whole represents the seeds of the Cordaitales[908]. It is, however, certain that some Platyspermic seeds were produced by Pteridosperms. No little confusion has been caused by the employment of the same generic names for petrified seeds and for casts and impressions affording no evidence as to similarity in anatomical characters. With a view to avoid the risks necessarily entailed by following this practice it is suggested that a clearer distinction should be drawn between genera based primarily on structural features and form-genera. The following notes on the genera _Cardiocarpus_, _Cordaicarpus_, _Cyclocarpon_, _Cycadinocarpus_, _Jordania_, and _Samaropsis_, may serve to illustrate some of the difficulties connected with the terminology of Palaeozoic seeds.