there are alot of theories as to the use of bolas, but no one knows for sure....it is mainly thought to be a weapon to hunt animals. the bolas would be presumably wrapped in rawhide, with a knot at the top(in the little depression), and a leather rope tied to it. a few bolas(more than one at least) would be tied together and swung over the head and thrown at animals legs to trip it.
the example i show above came from the Santa Fe river back in the mid nineties, right next to the boat ramp in two feet of water...i was testing my regulator and just started fanning, there it was, i couldn't believe it! the guys freaked cause i found a few in a lifetime find while they were getting the boats ready at the ramp

the one above is made of coral, very heavy
the identifying features usually include the following:
1. shaped roughly like an egg in most cases, some are round
2. one end will have a small dimple or depression pecked out, some just have a dime sized flat spot
3. usually will have a flat side(as seen in pic) possibly to make it sit next to another one while hanging
4. the end opposite the dimple end will usually be ground to a rounded point