Enemy #48 I can confirm is Anubis II - 'The second incarnation of Anubis. He'll do anything to protect the treasures of the underworld.'
Item # 32 is the Book of the Dead - 'Guarded by Anubis II in the City of Gold. It opens the entrance to the underworld.'
I'm guessing you find the plasma cannon in the Mothership area? I've barely been in there at all.
I'm almost 100% positive that all other missing entries are all to do with the final area of the game.
The Book of the Dead blinks faster when you are directly above the door to hell when fighting Olmec. Unfortunately I was fragged instinatly by brushing into the lower corner of him while trying to get him to dig down. Back to the drawing board!