The lanthanum spectrum was photographed in the 80-1240 Angstrom region on a
variety of vacuum spectrographs using triggered spark sources. The analysi
s of nine-times ionized lanthanum (La X) has led to revision of four previo
usly identified levels of the 5s5d configuration and established one new le
vel S-1(0) of the 5s6s configuration, four levels of the 5s4f configuration
, and nine out of twelve levels of the 5p4f configuration. The least square
s fitted parametric (LSF) and Hartree-Fock (HF) calculations interpret the
observed spectrum adequately. Fifty eight lines are now classified in La X,
out of which forty five are new lines.