It must be sufficiently obvious to the readers of the Geological Magazine that any modification of the original meaning of a descriptive term that may serve the purpose of enabling us to convey a specific idea with less chance of ambiguity is a distinct gain to both author and reader. This is especially the case when other specific terms are forthcoming to fill the vacancies in descriptive terminology caused by the restriction in meaning of the term in question, and when it is possible at the same time to supply a suitable generic term sufficiently comprehensive in its meaning to embrace the common characteristics of the whole.