This skull which when turned on, only melee attacks restore your shields can be found in "The Library" and requires a grenade jump (Throwing a grenade at your feet and the force of it should propel you higher) , It is located right at the start before you enter the big round room where the index is located. There are vents on the wall where flood come out of. With your back facing the entrance to the index chamber, the skull is located in the vent to your right, grenade jump on to the platform in front of it then jump normally into the vent, move towards the end of the vent and you should pick it up.
|Unlockable:||How to unlock:|
|Black Eye Skull||The Library, in the vent right before entering the index chamber.|