=Nomenclature.=--A family in zoology is an assemblage of related genera. The name of a family, for convenience, always ends in the patronymic _idæ_, and it is always derived from the leading genus, that is, the one best known or earliest studied. Thus all lampreys constitute the family _Petromyzonidæ_. An order may contain one or more families. An order is a division of a larger group; a family an assemblage of related smaller groups. Intermediate groups are often recognized by the prefixes sub or super. A subgenus is a division of a genus. A subspecies is a geographic race or variation within a species; a super-family a group of allied families. Binomial nomenclature, or the use of the name of genus and species as a scientific name, was introduced into science as a systematic method by Linnæus. In the tenth edition of his Systema Naturæ, published in 1758, this method was first consistently applied to animals. By common consent the scientific naming of animals begins with this year, and no account is taken of names given earlier, as these are, except by accident, never binomial. Those authors who wrote before the adoption of the rule of binomials and those who neglected it are alike "ruled out of court." The idea of genus and species was well understood before Linnæus, but the specific name used was not one word but a descriptive phrase, and this phrase was changed at the whim of the different authors. [Illustration: FIG. 239.--Horned Trunkfish, Cowfish, or Cuckold, _Lactophrys tricornis_ (Linnæus). Charleston, S. C.] =Nomenclature of Trunkfishes.=--Examples of such names are those of the West Indian trunkfish, or cuckold (_Ostracion tricorne_, Linnæus). Lister refers to a specimen in 1686 as "_Piscis triangularis capiti cornutu cui e media cauda cutanea aculeus longus erigitus_." This Artedi alters in 1738 to _Ostracion triangulatus aculeis duobus in capite et unico longiore superne ad caudam_. This is more accurately descriptive and it recognizes the existence of a generic type, _Ostracion_, or trunkfish, to cover all similar fishes. French writers transformed this into various phrases beginning "Coffre triangulaire à trois cornes," or some similar descriptive epithet, and in English or German it was likely to wander still farther from the original. But Linnæus condenses it all in the word _tricornis_, which, although not fully descriptive, is still a name which all future observers can use and recognize.