im missing a monster for the monster arena

in the omega dungeon i have black elemen, zaurus, spirir, maste courel, master tonberry, floating death puroburos, machea and im missing one i was wondering what it was

You're missing a master malboro, i think.

no it was halma, master malboro is in sin

What about those things that look like a tombstone? Sorry I don't know names.

EDIT: Here is a list from Gamefaqs:

Omega Dungeon
Zaurus - 1425 gil
Floating Death - 1897 gil
Black Element - 1560 gil
Halma - 1545 gil
Puroboros - 1455 gil
Spirit - 1950 gil
Machea - 2175 gil
Master Coeurl (page 2) - 3045 gil
Master Tonberry (page 2) - 3600 gil
Varuna (page 2) - 2670 gil