The extensive number of the species, and the difficulty of distinguishing them with a tolerable degree of certainty, has deterred Dr. Haller from adding so full and complete a list of synonyms to the plants of this genus as he has elsewhere done in that splendid work. Plate the 2d exhibits several elegant sorts of these lichens.

Linnæus, and the followers of his method, who seem to have established their generical character from Micheli’s discoveries, retain also his generical title. Micheli’s passion for the multiplication of species is no-where more conspicuous than in the plants of this genus, which he has most enormously augmented to the number of 298 species. The Swedish professor cannot be charged with this foible: it is one of the excellencies of his writings, that they inculcate the reverse. He has so far retrenched this genus, that in his general enumeration of plants he recounts only eighty species belonging to it. They are in this work divided into eight orders, according to the difference of appearance which they form by their facies externa, little or no regard being had to what are usually called the parts of fructification.

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.