Genera which are polymorphic in one country seem to be, with a few exceptions, polymorphic in other countries, and likewise, judging from Brachiopod shells, at former periods of time.
Herrialde batean poliformoak diren generoak beste herrialdeetan ere, salbuespen gutxirekin, poliformoak izaten direla dirudi, eta, maskordun brakiopodoak kontuan hartuz, lehenagoko garaietan ere.