II. MEDULLOSEAE. The term Medulloseae was first employed by Goeppert and Stenzel[236] for a family of Palaeozoic plants that appears to have reached its maximum development in the Permian period: the oldest representatives so far discovered are of Upper Carboniferous age. Our knowledge of the family is chiefly derived from a study of the anatomical characters of stems, and it is therefore on this basis that any grouping of genera or species should be attempted. Although there is little information with regard to the reproductive organs of _Medullosa_, the type-genus, it is certain that the Medulloseae are Pteridosperms differing from members of that group included in the Lyginopterideae in the presence of more than one stele in the stem, in the habit of the fronds, and in the structure of the rachis, as also in the structure of the seeds, though these organs bear a fairly close resemblance to the seeds of _Lyginopteris_ and _Heterangium_. The fronds of the Lyginopterideae are of the _Sphenopteris_ type while in the case of such species of _Medullosa_ as afford evidence of connexion between stems and leaves the latter have the characters of _Neuropteris_, _Alethopteris_, _Odontopteris_, _Linopteris_, and other form-genera usually included in the Neuropterideae. Dr Lotsy[237] speaks of _Lyginopteris_ and _Heterangium_ as members of the Sphenopteridophylla and assigns species of _Medullosa_ either to the Neuropteridophylla or to the Pecopteridophylla, the latter subdivision including species with fronds of the _Alethopteris_ type. There is, however, little doubt that other forms of leaves, such as _Odontopteris_ and possibly _Taeniopteris_, were borne on Medullosan stems. It is undesirable except in the absence of more trustworthy criteria to make use of so protean a feature as leaf-form as a basis of classification. The name Neuropterideae has been frequently employed for Pteridosperms other than the Lyginopterideae on the ground that the foliage of _Medullosa_ is represented by species assigned to form-genera included in the Neuropterideae. It is, however, preferable to restrict the family-name Neuropterideae to fronds and to speak of the second family of Pteridosperms as the Medulloseae, including the genera _Medullosa_, _Sutcliffia_, and _Rhexoxylon_. =MEDULLOSA.=