Linothorax design/construction

[Paullus Scipio]

"kai spolas anti thorakos" meaning "and spolas instead of thorax".So spolas is not a thorax,for Xenophon.

Exactly ! Spolas and Thorakes are different, of course. If you take the meanings I ascribed above, the phrase makes perfect sense.
'Leather tube-and-yoke coselet instead of metal body armour'
Elsewhere in the Anabasis, when speaking of the raising of the cavalry he says they were equipped with 'spolades kai thorakes' - leather tube-and-yoke corselets and and bronze breast plates, (because cavalry did not have shields, hence needed the body-armour.)
There is also the incident when racing the enemy to the summit of a hill, when a Hoplite complains that it's alright for Xenophon, who is mounted, to urge speed, while he has a heavy shield to carry. Xenophon dismounts, takes the man's shield, and rushes forward. He falls behind, because in addition to the shield he is burdened by his heavy 'cavalry' thorakes (breastplate, evidently a bronze muscle cuirass).The man's comrades shame him into taking back his shield.