but we ought to find after intervals, very long as measured by years, but only moderately long as measured geologically, closely allied forms, or, as they have been called by some authors, representative species;
baina, urtez neurturik oso luzeak izan arren geologikoki luze samarrak besterik ez diren tarteen ondoren, forma oso hurbilak, espezie errepresentagarriak, autore batzuek esaten dieten bezala, aurkitu behar ditugu;