_In any classificatory science names including more than two steps of the classification may be employed if it be found convenient._ LINNÆUS, in his canons for botanical nomenclature (Art. 212), says that the names of the class and the order are to be _mute_, while the names of the Genus and Species are _sonorous_. And accordingly the names {311} of plants (and the same is true of animals) have in common practice been binary only, consisting of a generic and a specific name. The class and the order have not been admitted to form part of the appellation of the species. Indeed it is easy to see that a name, which must be identical in so many instances as that of an Order would be, would be felt as superfluous and burthensome. Accordingly, Linnæus makes it one of his maxims[47\4], that the name of the Class and Order must not be expressed but understood, and hence, he says, Royen, who took _Lilium_ for the name of a Class, rightly rejected this word as a generic name, and substituted _Lirium_ with the Greek termination. [Note 47\4: _Phil. Bot._ s. 215.] Yet we must not too peremptorily assume such maxims as these to be universal for all classificatory sciences. It is very possible that it may be found advisable to use _three_ terms, that of Order, Genus, and Species in designating minerals, as is done in Mohs's nomenclature, for example, _Rhombohedral Calc Haloide_, _Paratomous Hal Baryte_. It is possible also that it may be found useful in the same science (Mineralogy) to mark some of the steps of classification by the termination. Thus it has been proposed to confine the termination _ite_ to the Order _Silicides_ of Naumann, as Apophyll_ite_, Stilb_ite_, Leuc_ite_, &c., and to use names of different form in other orders, as Talc _Spar_ for Brennerite, Pyramidal Titanium _Oxide_ for Octahedrite. Some such method appears to be the most likely to give us a tolerable mineralogical nomenclature. APHORISM XVIII. _In forming a Terminology, words may be invented when necessary, but they cannot be conveniently borrowed from casual or arbitrary circumstances_[48\4]. [Note 48\4: I may also refer to _Hist. Sc. Id._ b. viii. c. ii. sec. 2, for some remarks on Terminology.]