In view of the fact that the generic names _Cardiocarpus_, _Cordaicarpus_, and other designations have been applied to casts and impressions which cannot be distinguished by any constant or important feature it is proposed to adopt the name _Cordaicarpus_ for platyspermic seeds, preserved as casts or impressions, having a comparatively narrow border enclosing an ovate or cordate-ovate nucule; the base is either rounded or cordate. The choice between _Cordaicarpus_ and _Samaropsis_ depends on the breadth of the border. _Cordaicarpus_, though more suggestive of a Cordaitean alliance, may in some cases be a Pteridosperm seed. _Cordaicarpus Cordai_ (Geinitz). Lenticular seeds more or less orbicular or broadly ovate (fig. 502, C, D), often slightly cordate at the base of the nucule and with a broadly acute apex: the border is narrow or sometimes hardly represented as in the seeds described by Berger as _Rhabdocarpus ovoides_, a species similar to but more oval than _Cordaicarpus Cordai_. The latter species[1016] occurs in several coalfields in Britain, France, Germany, and elsewhere. Fig. 502, C, shows a good example from the Middle Coal Measures of Yorkshire, 9 mm. long by 8 mm. broad; on the very slightly cordate nucule are several faint ribs converging towards the base and apex and between them fine striations, characters too indistinct to be reproduced in the natural-size drawing. The flat border represents the sclerotesta. The seed shown in fig. 502, D, from the Westphalian series of Warwickshire belongs to the same species or is a closely allied type: the faint suggestion of reticulation on its surface might be regarded as a reason for referring it to _C. areolatus_ Boul.[1017], a form characterised by a reticulation on the testa, described by Zeiller[1018] and other authors. This reticulation is, however, in some cases at least, formed by crumpling and splitting of the superficial carbonised film into more or less regular meshes: the figured specimen occurs with several other seeds of the same type, most of which have a smooth surface. Dr Kidston tells me that a recent critical examination of seeds in his collection leads him to regard some specimens (_e.g._ fig. 502, D) previously referred by him to _C. Cordai_ as identical with _Carpolithes membranaceus_ Goepp.[1019] [Illustration: Fig. 505. _Cordaicarpus Cordai._ Cuticle of the testa. (Kidston Collection.)] The photograph reproduced in fig. 505 shows the result of chemically treating the carbonised cuticle of a seed of _Cordaicarpus Cordai_, a method little used as yet in the case of Palaeozoic plants but which may be useful in distinguishing seeds which cannot be satisfactorily separated by microscopic features. The superficial cells have very thick walls and present an appearance similar to that of the sclerous cells in the testas of some petrified specimens.