pari animo

I have come across an excerpt in Wheelock's Loci immutati 9 that is giving me a little trouble. It is a line from Cicero's Tusculanae disputationes 1.42.
Pari animo Lacedaemonii in Thermopylis occiderunt,...
I see that pari is given as the verb pario in the 2nd sg pres imperat act in the Perseus word study tool. This makes absolutely no sense to me. I take as the ablative of par, paris so that the meaning would be "in like spirit/mind." The comparison would thus be with the aforementioned legions who set off for a place not knowing if they would ever come back. Am I right?
 
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