Plants resembling in habit the recent Equisetums. Stems simple or branched, divided into distinct nodes and internodes, the latter marked by longitudinal ridges and grooves; from the nodes are given off leaf-sheaths consisting of linear-lanceolate uninerved segments coherent basally, but having the form of free narrow teeth for the greater part of their length. The long free teeth are usually spread out in the form of a cup and not adpressed to the stem, the tips of the teeth are often incurved. The sporangia are borne on peltate sporangiophores attached to the stem between whorls of sterile leaves. Our knowledge of _Phyllotheca_ is unfortunately far from complete. The chief characteristic of the vegetative shoots consists in the cup-like leaf-sheaths; these are divided up into several linear segments, which differ from the teeth of an _Equisetum_ leaf-sheath in their greater length and in their more open and spreading habit of growth. The large loose sheaths of the fertile shoots of some recent Horse-tails bear a certain resemblance to the sheaths of _Phyllotheca_. The diagnosis of the fertile shoots is founded principally on some Permian specimens of the genus described by Schmalhausen from Russia[546] and redescribed more recently by Solms-Laubach[547]. Prof. Zeiller[548] has, however, lately received some examples of _Phyllotheca_ from the Coal-Measures of Asia Minor which bear strobili like those of the genus _Annularia_, a type which is dealt with in the succeeding chapter. A description of a few species will serve to illustrate the features usually associated with this generic type, as well as to emphasize the unsatisfactory state of our knowledge as to the real significance of such supposed generic characteristics.