Section 27. When an instrument by which a person transfers or conveys by authority of law the real estate of another is left for record, the register shall enter in the entry book and grantor index both the name of the nominal grantor and that of the real party in interest, if appearing therein, otherwise he shall enter such party as ”unknown”, under the letter U. When notice of the filing of a petition for partition or of amendment thereof, or a copy of a decree in partition is left for record, he shall enter in the entry book and in both the grantor and grantee indexes the names of all persons whose estates plainly appear to be affected thereby.