It was the custom of some of the earliest writers, in spite of their habit of using the names of recent Flowering plants for extinct Palaeozoic species of Vascular Cryptogams, to adopt also general and comprehensive terms. We find such a name as _Lithoxylon_ employed by Lhwyd[159] in 1699 as a convenient designation for fossil wood. [Sidenote: THE RULE OF PRIORITY.] One of the most important and frequently disputed questions associated with the naming of species is that of priority. No name given to a plant in pre-Linnaean days need be considered, as our present system of nomenclature dates from the institution of the binominal system by Linnaeus. As a general rule, which it is advisable to follow, the specific name which was first given to a plant, if accompanied by a figure or diagnosis, should take priority over a name of later date. If _A_ in 1850 describes a species under a certain name, and in 1860 _B_ proposes a new name for the same species, either in ignorance of the older name or from disapproval of _A_’s choice of a specific term, the later name should not be allowed to supersede _A_’s original designation. Such a rule is not only just to the original author, but is one which, if generally observed, would lead to less confusion and would diminish unnecessary multiplication of specific names. Some writers would have us conform in all cases to this rule of priority, which they consistently adhere to apart from all considerations of convenience or long-established custom. There are, however, cogent reasons for maintaining a certain amount of freedom. While accepting priority as a good rule in most cases, it is unwise to allow ourselves to be too servile in our conformity to a principle which was framed in the interests of convenience, if the strict application of the rule clearly makes for confusion and inconvenience. A name may have been in use for say eighty years, and has become perfectly familiar as the recognised designation of a particular fossil; it is discovered, however, that an older name was proposed for the same species ninety years ago, and therefore according to the priority rule, we must accustom ourselves to a new name in place of one which is thoroughly established by long usage. From a scientific point of view, the ideal of nomenclature is to be plain and intelligible. To prefer priority to established usage entails obscurity and confusion. If priority is to be the rule which we must invariably obey in the shadowy hope that by such means finality in nomenclature[160] may be reached, it becomes necessary for the student to devote no inconsiderable portion of his time to antiquarian research, with a view to discover whether a particular name may be stamped with the hallmark of ‘the very first.’ While admitting the advisability of retaining as a general principle the original generic or specific name, the extreme subservience to ‘the priority craze’ without regard to convenience, would seem to lead