This well-known genus presents a nomenclatorial problem apparently even simpler than that of Mortoniceras, dealt with in the first article of the present series, yet I can foresee considerable opposition to the views here put forward. It is, of course, agreed that “names now current are not to be discarded unless the reasons for change show a clear-cut necessity” (Opinion 93); but since “priority of actual date” is quoted as an example of such necessity, I consider that we shall have to change our present interpretation of Pachydiscus, however irksome the change may be to some.1