_BB._ _LECANORALES._ This second group of Cyclocarpineae is distinguished by the marginate apothecium, a thalline layer providing a protecting amphithecium. The lecanorine apothecium is of a more or less soft and waxy consistency, and though the disc is sometimes almost black, neither hypothecium nor parathecium is carbonaceous as in _Lecidea_. The affinity of _Lecanora_ is with sect. _Biatora_, and development must have been from a biatorine form with a persistent thallus. The margin or amphithecium varies in thickness: in some species it is but scanty and soon excluded by the over-topping growth of the disc, so that a zone of gonidia underlying the hypothecium is often the only evidence of gonidial intrusion left in fully formed fruits. The marginate apothecium has appeared once and again as we have seen. It is probable however that its first development was in this group of lichens, and even here there may have been more than one origin as there is certainly more than one phylum. _aa._ _COURSE OF DEVELOPMENT._ At the base of the series, the thallus is of the crustaceous type somewhat similar to that of _Lecidea_, but there are none of the very simple primitive forms. _Lecanora_ must have originated when the crustaceous lecideine thallus was already well established. Its affinity is with _Lecidea_ and not with any fungus: where the thallus is evanescent or scanty, its lack is due to retrogressive rather than to primitive characters. _bb._ _LECANORACEAE._ A number of genera have arisen in this large family, but they are distinguished mainly if not entirely by spore characters, and by some systematists have all been included in the one genus _Lecanora_, since the changes have taken place within the developing apothecium. There is one genus, _Harpidium_, which is based on thalline characters, represented by one species, _H. rutilans_, common enough on the Continent, but not yet found in our country. It has a thin crustaceous homoiomerous thallus, the component hyphae of which are divided into short cells closely packed together and forming a kind of cellular tissue in which the algae are interspersed. The dorsiventral stratose arrangement prevails however in the other genera and a more or less amorphous “decomposed” cortex is frequently present. The medulla rests on the substratum. With the stouter thallus, there is slightly more variety of crustaceous form than in Lecideaceae: there occurs occasionally an outgrowth of the thalline granules as in _Haematomma ventosum_ which marks the beginning of fruticulose structure. Of a more advanced structure is the thallus of _Lecanora esculenta_, a desert lichen which becomes detached and erratic, and which in some of its forms is almost coralline, owing to the apical growth of the original granules or branches: a more or less radiate arrangement of the tissues is thus acquired.