_Cardiocarpus_. Brongniart[909] proposed the name _Cardiocarpon_ in 1828 for Upper Carboniferous seeds described as compressed lenticular, cordiform or reniform ‘fruits’ with an acute apex: in his later work[910] he recognised their true morphological nature and gave an account of some exceptionally well-preserved examples from Grand’ Croix. Brongniart in common with other authors believed _Cardiocarpus_ seeds to belong to Cordaitean plants, a view that in several cases is based on conclusive evidence. The specimen represented in fig. 501, D, illustrates the characteristic form of a cast of a _Cardiocarpus_ seed, and the sections shown in fig. 501, A and B, are from an identical or a very closely allied species. The generic characters are: (i) the presence of a narrow flattened border or wing surrounding a platyspermic nucule, (ii) the cordiform base and more or less pointed apex, (iii) the differentiation of the testa into a sarcotesta and sclerotesta free from the nucellus except at the base, (iv) the ‘tent-pole’ prolongation of the prothallus (fig. 510, A, _b_) and the presence of a fairly large pollen-chamber, _pc_, (v) the occurrence of two sets of vascular bundles, an inner nucellar series and two double vascular strands (fig. 500, A, _v_, B) which are given off from the main supply before it reaches the sclerotesta. The term _Cardiocarpus_ as used by Brongniart signifies a type of seed possessing both certain anatomical and external characters. The proposal is to restrict the generic appellation to seeds exhibiting definite structural features agreeing in essentials with _Cardiocarpus sclerotesta_ and _C. drupaceus_. _Cordaicarpus_. This name was first employed by Geinitz[911] in the form _Cordaicarpon_, the type-species being _C. Cordai_ (fig. 502, C) from the Coal Measures of Germany, a seed referred by the author of the genus to _Cordaites principalis_ but, as Kidston has pointed out, there is evidence that this correlation may be incorrect: there is, however, no doubt as to its Cordaitean parentage. Specimens included in this genus agree closely with species of _Cardiocarpus_, but they are usually described as being distinguished by the absence of a flat border and by a more rounded and less cordate base. In the example of _Cordaicarpus Cordai_ shown in fig. 502, C, and in other species assigned by authors to this genus there is a narrow border and the form of the base is an inconstant character. As Kidston[912] and other authors point out, there are no definite and constant characters by which to distinguish _Cardiocarpus_ from _Cordaicarpus_ as regards the form of the seeds preserved as casts or impressions. A further account of _Cordaicarpus_ is given on a later page.