lyoocobrium, spelled by ear
heard as lyoocobrium
spelled leucobryum
Everything here is a fair phonetic guess and none of it is the spelling. It is leucobryum.
What the ear did
Two Greek letters have been written the English way at once: the eu of leukos as yoo, and the upsilon of bryon as i. The name kept the transliteration it was given in the eighteenth century, and neither half moved.
L-E-U-C-O-B-R-Y-U-M
The full entry for leucobryum covers the name itself.