The 14 elements of the sixth period of the long form of the periodic table are known as ___________.

The lanthanides and actinides are together known as inner transition elements. Both the lanthanides and actinides are placed in two rows below the main body of the table. Hence, 14 elements of the sixth period of the long form of the periodic table are known as Lanthanides. This lanthanide series starts from atomic number 58 and ends at atomic number 71.