Section 20. A person who was not made a party and has not appeared and who claims part of the land as a co-tenant with any of those who were parties to the action, shall, if the share so claimed was unknown or not allowed and left for him in the process of partition, be concluded by the decree so far as it relates to the partition, but may, subject to section eighteen, bring an action for the share claimed by him against each of the persons holding any part of the land under the decree for partition; and, if he prevails, shall recover against each the same proportion of the part so held that he was entitled to claim out of all the land before the partition. If the partition was made by sale, he may in like manner recover his portion of the proceeds, as provided in the preceding section.