1. _Lichenes leprosi tuberculati._ 2. _Lichenes leprosi scutellati._ 3. _Lichenes imbricati._ 4. _Lichenes foliacei._ 5. _Lichenes coriacei._ 6. _Lichenes scyphiferi._ 7. _Lichenes fructiculosi._ 8. _Lichenes filamentosi._ Dr. Dillenius, in his most elaborate work, intituled, _Historia Muscorum_, has divided this Michelian genus into three, under the names of _usnea_, _coralloides_, and _lichenoides_. Under the word _usnea_ he comprehends the hairy tree-mosses, among which are the _usnea_ of the shops, and the true _usnea_ of the Arabians. Of these he describes sixteen species. Under _coralloides_ he describes thirty-nine species, among which are the cup-mosses, and many others, disposed according to the following scheme: Ordo I. _Fungiformia, non tubulosa, nec ramosa._ 5. Ordo II. _Scyphiformia, tubulosa, simplicia et prolifera._ Series 1. _Scyphis perfectioribus._ 13. Cup-mosses. Series 2. _Scyphis imperfectis._ 20. Horned mosses. Ordo III. _Ramosa fruticuli specie summitatibus acutis multifariam divisis._ Series 1. _Species tubulosæ._ 30. Tubulous coralline mosses. Series 2. _Species solidæ._ 39. Solid coralline mosses; among which is the _orchel_. The genus of _lichenoides_ contains 135 species, disposed according to the following scheme: Ordo I. _Species aphyllæ mere crustaceæ._ {1. _Tuberculosæ._ 8. {2. _Scutellatæ._ 18. {1. _Gelatinosæ tuberculosæ et scutellatæ._ 35. Ordo II. _Species foliosæ._ {2. _Aridiores et exsuccæ, scutellatæ._ 100. {3. _Aridiores peltatæ et clypeatæ._ 121. These plants are not only largely described, and accompanied with the most perfect assemblage of synonyms; but every species is accurately figured, and many of them in various views, and at different ages of their growth; by which this laborious work, notwithstanding it is conversant upon the minutest, and consequently the most abstruse parts of botany, may nevertheless be justly esteemed, without any exaggeration, one of the most complete works extant of the kind. Dr. Hill, in his History of Plants, has disposed them into five genera, under the following names: 1. _Usnea_, comprehending the hairy tree-mosses; 2. _Platysma_, flat-branched tree-mosses, the lungwort, and others; 3. _Cladonia_, containing the orchel and coralline-mosses; 4. _Pyxidium_, the cup-mosses; 5. _Placodium_, the crustaceous mosses. The plants of this extensive genus are very different in their form, manner of growing, and general appearance: on which account those authors, who preserve them under the same name, saw the propriety and necessity of arranging them into different orders and subdivisions, that the species might be distinguished with greater facility. Upon the same principle Dr. Dillenius and Dr. Hill have formed them into several genera.