In all 47 genera and 230 species of fishes were known from the whole world in 1738.
The cetaceans, or whales, constitute a fifth order, Plagiuri, in Artedi's scheme.
As examples of the nomenclature of species I may quote:
"Zeus ventre aculeato, cauda in extremo circinata." This polynomial expression was shortened by Linnæus to Zeus faber. The species was called by Rondelet "Faber sive Gallus Marinus" and by other authors "Piscis Jovii." "Jovii" suggested Zeus to Artedi, and Rondelet's name faber became the specific name.
"Anarhichas Lupus marinus nostras." This became with Linnæus "Anarhichas lupus."
"Clupea, maxilla inferiore longiore, maculis nigris carens: Harengus vel Chalcis Auctorum, Herring vel Hering Anglis, Germanis Belgis." This became Clupea harengus in the convenient binomial system of Linnæus.
The great naturalist of the eighteenth century, Carl von Linné, known academically as Carolus Linnæus, was the early associate and close friend of Artedi, and from Artedi he obtained practically all his knowledge of fishes. Linnæus, professor in the University of Upsala and for a time its rector, primarily a botanist, was a man of wonderful erudition, and his great strength lay in his skill in the orderly arrangement of things. In his lifetime, his greatest work, the "Systema Naturæ," passed through twelve editions. In the tenth edition, in 1758, the binomial system of nomenclature was first consistently applied to all animals. For this reason most naturalists use the date of its publication as the beginning of zoological nomenclature, although the English naturalists have generally preferred the more complete twelfth edition, published in 1766. This difference in the recognized starting-point has been often a source of confusion, as in several cases the names of species were needlessly changed by Linnæus and given differently in the twelfth edition. In taxonomy it is not nearly so important that a name be pertinent or even well chosen as that it be stable. In changing his own established names, the father of classification set a bad example to his successors, one which they did not fail to follow.
In Linnæus' system (tenth and twelfth editions) all of Artedi's genera were retained save Lepturus, which name was changed to Trichiurus. The following new genera were added: Chimæra, Tetraodon, Diodon, Centriscus, Pegasus, Callionymus, Uranoscopus, Cepola, Mullus, Teuthis, Loricaria, Fistularia, Atherina, Mormyrus, Polynemus, Amia, Elops. The classification was finally much altered: the Chondropterygia and Branchiostegi (with Syngnathus) being called Amphibia Nantes, and divided into two groups—Spiraculis compositis and Spiraculis solitariis. The other fishes were more naturally distributed according to the position of the ventral fins into Pisces Apodes, Jugulares, Thoracici, and Abdominales. The Apodes of Linnæus do not form a homogeneous group, as members of various distinct groups have lost their ventral fins in the process of evolution. But the Jugulares, the Thoracici, and the Abdominales must be kept as valid categories in any natural system.
Linnæus' contributions to zoology consisted mainly of the introduction of his most ingenious and helpful system of bookkeeping. By it naturalists of all lands were able to speak of the same species by the same name in whatever tongue. Unfortunately, ignorance, carelessness, and perversity brought about a condition of confusion. For a long period many species were confounded under one name. This source of confusion began with Linnæus himself. On the other hand, even with Linnæus, the same species often appeared under several different names; in this matter it was not the system of naming which was at fault. It was the lack of accurate knowledge, and sometimes the lack of just and conscientious dealing with the work of other men. No system of naming can go beyond the knowledge on which it rests. Ignorance of fact produces confusion in naming. The earlier naturalists had no conception of the laws of geographical distribution. The "Indies," East or West, were alike to them, and "America" or "India" or "Africa" was a sufficiently exact record of the origin of any specimen.
Moreover, no thought of the geological past of groups and species had yet arisen, and without the conception of common origin, the facts of homology had no significance. All classification was simply a matter of arbitrary pigeon-holing the records of forms, rather than an expression of actual blood relationship. To this confusion much was added through love of novelty. Different authors changed names to suit their personal tastes regardless of rights of priority. Amia was altered to Amiatus by Rafinesque in 1815 because it was too short a name. Hiodon was changed to Amphiodon because it sounded too much like Diodon, Batrachoides to Batrictius because βατράχος means a frog, not a fish, and other changes even more wanton were introduced, to be condemned and discarded by the more methodical workers of a later period. With all its abuses, however, the binomial nomenclature made possible systematic zoology and botany, and with the "Systema Naturæ" arose a new era in the science of living organisms.