The squamulose type is well represented in _Lecanora_, and the species with that form of thallus have frequently been placed in a separate genus, _Squamaria_. These squamules are never very large; they possess an upper, somewhat amorphous, cortex; the medulla rests on the substratum, except in such a species as _Lecanora lentigera_, where they are free, a sort of fibrous cortex being formed of hyphae which grow in a direction parallel with the surface. In none of them are rhizinae developed. _cc._ _PARMELIACEAE._ The chief advance, apart from size, of the squamulose to the foliose type is the acquirement of a lower cortex along with definite organs of attachment which in Parmeliaceae are invariably rhizoidal and are composed of compact strands of hyphae extending from the cells of the lower cortex. In the genus _Parmelia_ rhizinae are almost a constant character, though in a few species, such as _Parmelia physodes_, they are scanty or practically absent. It is not possible, however, to consider that these species form a lower group, as in other respects they are highly evolved, and rhizinae may be found at points on the lower surface where there is irritation by friction. Soredia and isidia occur frequently and, in several species, almost entirely replace reproduction by spores. In one or two northern or Alpine species, _P. stygia_ and _P. pubescens_, the lobes are linear or almost filamentous. They are retained in _Parmelia_ because the apothecia are superficial on the fronds which are partly dorsiventral, and because rhizinae have occasionally been found. Some of the _Parmeliae_ attain to a considerable size; growth is centrifugal and long continued. Two monotypic genera classified under Parmeliaceae, _Physcidia_ and _Heterodea_, are of considerable interest as they indicate the bases of parallel development in _Parmelia_ and _Cetraria_. The former, a small lichen, is corticate only on the upper surface, and without rhizinae; and from the description, the cortex is of a fastigiate character. The solitary species grows on bark in Cuba; it is related to _Parmelia_, as the apothecia are superficial on the lobes. The second, _Heterodea Mülleri_, a soil-lichen from Australasia, is more akin to _Cetraria_ in that the apothecia are terminal. The upper surface is corticate with marginal cilia, the lower surface naked or only protected by a weft of brownish hyphae amongst which cyphellae are formed; pseudocyphellae appear in _Cetraria_. The genus _Cetraria_ contains very highly developed thalline forms, either horizontal (subgenus _Platysma_), or upright (_Eucetraria_). Rhizinae are scanty or absent, but marginal cilia in some upright species act as haptera. _Cetraria aculeata_ is truly fruticose with a radiate structure.