@abc.abstractmethod<EOL><INDENT>def get_agencies_by_parent_genus_type(self, agency_genus_type):<DEDENT>
return<EOL>
Gets an ``AgencyList`` corresponding to the given agency genus ``Type`` and include any additional agencies with genus types derived from the specified ``Type``.

        In plenary mode, the returned list contains all known agencies
        or an error results. Otherwise, the returned list may contain
        only those agencies that are accessible through this session.

        :param agency_genus_type: an agency genus type
        :type agency_genus_type: ``osid.type.Type``
        :return: the returned ``Agency`` list
        :rtype: ``osid.authentication.AgencyList``
        :raise: ``NullArgument`` -- ``agency_genus_type`` is ``null``
        :raise: ``OperationFailed`` -- unable to complete request
        :raise: ``PermissionDenied`` -- authorization failure

        *compliance: mandatory -- This method must be implemented.*