Article: F. A. Quenstedt's trinomial nomenclature of Jurassic ammonites

In an early attempt to incorporate infraspecific, varietal categories into conventional, morphodescriptive Linnaean taxonomy, Quenstedt in 1845 introduced an idiosyncratic trinominal nomenclature that has bedevilled ammonite taxonomy ever since. The trinomina consist of ordinary binomina to which were added third names in the same adjectival form as the specific epithets themselves. The problem has been whether these third names should be construed as of subspecific rank, governed by the International Code of Zoological Nomenclature, or of infra-subspecific varietal rank, which is not. Quenstedt's exposition of the difference in principle between natural species and their variants was entirely clear, but its recognition in fossils has in practice to be subjective. Intended to be varietal, he used the same third names repeatedly, making no attempt to avoid homonymy under the generic name Ammonites. Subsequent revisers, judging Quenstedt's trinominally named taxa to be specifically distinct, have been faced with unending problems of homonymy. Two comprehensive solutions present themselves. The first, put forward by H. Houlder in 1958, is to declare all of Quenstedt's third names to be of infrasubspecific rank and hence not available in formal Linnaean nomenclature. The second, proposed here, is to declare all the trinomina to be in principle available at subspecific rank. We present the case for this solution as the basis for an application for its ratification to the International Commission on Zoological Nomenclature (ICZN).