often of considerable size and in all cases of complex structure, agreeing in many respects with those of existing Cycads, while other fronds, or in some cases it may be other pinnae, bore microsporangia similar in form to the sporangia of Ferns. _a. Microsporangia._ _Neuropteris._ A. _Neuropteris heterophylla[292]._ Several examples of supposed fertile specimens of _Neuropteris_ are recorded in palaeobotanical literature, but it was not until 1887 that any satisfactory specimen was discovered. In that year Kidston[293] described a specimen of _Neuropteris heterophylla_ from the Lower Coal Measures of Scotland in which slender forked branchlets bear small bodies at their tips some of which appear to represent four-valved organs (fig. 421, D), though the imperfect state of preservation renders impossible any definite pronouncement as to their structure. To the specimen are attached a few sterile pinnules, showing that it is a portion of a frond of _N. heterophylla_ characterised by the substitution of reproductive organs for pinnules. The subsequent discovery of seeds attached to pinnae of the same species afforded strong presumptive evidence, almost amounting to proof, of the microsporangial nature of the Scotch specimen. For this specimen, although no precise diagnosis is possible, Dr P. Bertrand[294] has proposed the generic name _Neurotheca_. In 1911 the Abbé Carpentier[295] described some small ovoid bodies, 1–1·5 mm. long, from the Coal Measures of France arranged in groups of 4 to 6 and in some cases said to be borne on a slender pedicel which he found in association with _N. heterophylla_ and compared with sporangia described by Lesquereux from the Coal Measures of Arkansas as _Sorocladus stellata_[296]. These supposed microsporangia have recently been assigned by Bertrand[297] to _Sphenophyllum_. [Illustration: Fig. 421. A. _Potoniea adiantiformis_ Zeill. (very slightly enlarged). B. Microsporangia of _Potoniea_ (enlarged). C. _Linopteris obliqua_; side-view of microsporophyll. D. _Neuropteris heterophylla_, pinnules and microsporangia (?). E. _Linopteris obliqua_, surface-view of microsporophyll. (A, C, E, after P. Bertrand; B, after Carpentier; D, after Kidston.)] B. _Neuropteris gigantea_, etc. _Potoniea_, Zeiller.