From the Internet (Some of the following anyway, some comes from catching a boatload of each species
Sharpnose Shark seldom gets to 48", frequently caught in the 36" range, known in NC waters in early September as a prelude to Drum fishing to come. It can bite you. Good with Children. Has white spots on back and sides.
Blacktip Shark can approach 6', most common Shark taken in Florida waters
, will feed on Sharpnose Sharks as mentioned by Geo, if a decent size one bites you, you will be on the way to the emergency room. No white spots on back and side.