Once you discover it was Kabuto, the floor will drop out and down you will fall into the cave below. (If nothing happens, you put the puzzle together wrong) Inside are a bunch of Pokedex called Unown. They have no gender, but they do have many different shapes. Don't get confused though, they all have the same Pokedex entry.

To unlock more shapes you will have to surf, strength, break rocks, towards the 3 other entrances to the cave (Like the Kabuto one where there is a puzzle to solve.) You can find them by surfing on the Lower Level of Union Cave. You need Strength to get two of them.

Exit the cave and a Scientist will upgrade your Pokedex for you. Now after you catch a Annon shape it will be recorded under here and you can take a look to see which ones you have by pressing Select while in the Pokedex and then choosing the last option.

After collecting all 26 Unown, talk to the scientist again and he will let you print out your Unown shapes.