The considerable range in size and form among Cordaitean leaves as well as the obvious dependence on conditions of preservation or growth of such a relatively unimportant feature as the presence or absence of the so-called false or interstitial veins—the variability of which has been demonstrated in several instances—renders specific determination exceedingly difficult. The following species are briefly described rather with a view to illustrate the nature of the characters employed by authors than as implying the existence of so many well-defined types. _Cordaites principalis_ (Germar). This species was founded[568] on a large specimen from the Coal Measures of Wettin showing a fan-like cluster of longitudinally torn and partially overlapping leaves spread out in the position that would be assumed on the compression of a shoot with a close spiral phyllotaxis. This form of _Cordaites_ is the most abundant in the British Coal Measures. The broadly linear lamina is characterised by an obtuse apex (fig. 466, A), a tendency to split into strips, close-set parallel ribs, the stouter ribs or veins separated from one another by 2–3 or it may be as many as 5 finer ribs or interstitial ‘veins.’ A statement by Weiss that in Germar’s type-specimen the longitudinal ribbing of the lamina is very imperfectly preserved confirms the scepticism that is justly felt as to the validity of this character as a satisfactory specific criterion. [Illustration: Fig. 466. A. _Cordaites principalis_, part of leaf. _B. Artisia_ _transversa_, pith-cast. C. _Cordaites principalis_, branch with leaf-scars. (A, ⅖ nat. size; B, C, nat. size; Kidston Coll.)] The incomplete example shown in fig. 466, A, is 19·5 cm. long and has a maximum breadth of 3·5 cm., but the complete leaf was much larger and tapered gradually to the comparatively broad and slightly concave or amplexicaul base. The narrow elliptical proximal end of a specimen figured by Kidston[569] from the Middle Coal Measures of Yorkshire is 2·8 cm. broad indicating that the tangentially expanded leaf-scars on a branch recently deprived of its foliage must have been a conspicuous feature. In his synonymy of this species Kidston[570] includes _Knorria taxina_, a species founded by Lindley and Hutton[571] on a piece of stem from the Coal Measures of Newcastle. The type-specimen, as Mr Howse[572] states, is much larger than the published drawing and closely resembles in the decurrent leaf-bases with broad apices the piece of stem represented in fig. 466, C, which Kidston identifies as _C. principalis_. Geinitz[573] refers to this species the seeds named _Cordaicarpus Cordai_ (Gein.), but there is no evidence of connexion. Kidston[574] points out that this seed is rare in Britain: he believes that _Cordaianthus Pitcairniae_ (Lind. and Hutt.) is probably the inflorescence of _C. principalis_.