Google is your friend
That link has lots of pictures of shovelnose cats on google.
If its a lima shovelnose, they get around 12 inches, according to planet catfish. If that is what you have, the 55g won't be big enough. At 13 inches wide, the 55g won't be wide enough for when this fish gets full grown.
Lima
Also, your 55g is a bit overstocked....I'd only put 1 oscar in a 55g...2 in a 75g....
I hope its not a Tiger shovelnose....they get huge!
Tiger