Kidstoni_ founded on a seed originally identified by Kidston[1055] as _Rhabdocarpus multistriatus_ Sternb. which, though probably a distinct species, is of the same general type as _C. sulcatus_ Sternb. The cast represented in fig. 506, A, from the Middle Coal Measures of Yorkshire is 3·5 cm. long and has 18 regular longitudinal ribs: it is radially symmetrical and does not conform in this respect to Arber’s definition of _Platyspermum_. In many cases, _e.g._ the flattened seed figured by Kidston as _Rhabdocarpus multistriatus_, it is impossible to determine the symmetry of the seed. The old generic name _Carpolites_, _Carpolithes_ or _Carpolithus_ has been used in a very wide sense and does not connote any well-defined features; it should be reserved, in the form _Carpolithus_ as used by Linnaeus, for seeds that cannot be assigned to a systematic position or which do not exhibit any distinctive characters worthy of emphasis by the institution of a special name. The generic term _Holcospermum_, recently proposed by Nathorst[1056], is a suitable name for this type of seed; as defined by the author, it includes seeds that may be radiospermic or platyspermic. Specimens of the type-species, _H. dubium_[1057],from the Lower Carboniferous beds of Spitzbergen, agree closely in size and shape with some examples of _Rhynchogonium_ and _Boroviczia_, but they are distinguished by prominent ribs extending the whole length of the cast. In some seeds similar to _H. sulcatum_ the ribs form sharp ridges, but the difference between rounded and sharp ridges is often determined by the method of preservation: a specimen deprived of its outer flesh would form a cast more sharply ribbed than a seed in which the sarcotesta had been moulded on to the ribbed sclerotesta. On the other hand some ribs are formed by blunt sclerotestal folds as in _Colpospermum_: both types of ribbing are included in the genus _Holcospermum_. ii. _Other Genera._ =Malacotesta.= Williamson. This generic name was instituted by Williamson[1058] for a petrified seed from the Coal Measures of Lancashire which he named _Malacotesta oblonga_: the type-specimen is a small seed 6–7 mm. long characterised by a thick fleshy integument. The structure is however insufficiently known to admit of a satisfactory comparison of the imperfectly preserved specimen figured by Williamson with other types. =Thysanotesta.= Nathorst. Nathorst[1059] founded this genus on a single seed from the Lower Carboniferous plant-beds of Spitzbergen which exhibits features sufficiently distinctive to justify its recognition as the type of a separate genus.