Bigsmoke, that black one at the top is actually a partially-prepped buffalo horn: even with about half the raw horn scraped away, further down it is still too thick to flatten without a lot of work. That one is roughed out and will eventually be a copy of a horn that was a battlefield pick-up taken home by a Brit during the War of 1812.
Ebony will work for a baseplug--I made the base plugs for a couple of St. Louis horns with the ivory/bone inlet into the ebony . . . then I got to see one and realized the ebony and ivory were thick veneers inlaid into the base material (poplar I suspect). Hey, if there is a hard way to do something, I not only do it but find a way to make it harder!
The black one at 3 o'clock is another buffalo horn. I was working on it for a friend when he passed away; I think eventually I'll finish it and make it a dedicated horn for a later (1830s-1850s) bag set. My current bag is a copy of a bag with provenance going back to sometime in the 1790s, and not quite right for the western fur trade--and there are a lot of things I don't like about it. But I've been living with it since I made the horn I usually carry, sometime in the late '90s, so I'll probably keep the old thing.
(Just as an aside: early summerish, I posted a buffalo horn I'd recently finished. The guy who bought it liked it a lot, and commented how light it was, so when I started the next one I weighed it before I started, and again after I had most of the shaping and scraping done. There was roughly a 70% drop in weight so far.)
That funny shaped horn at 6 o'clock is probably going to wind up getting smushed. It reminds me of a carved flattened horn I saw in a museum years ago, and I think it would be an interesting project to flatten and carve it.
The one centered at 9 o'clock is nearly straight. Normally I'd take a horn like that and cut it into rings to turn for a banded horn, but this is too thin. I think it has a future as a blowing horn, maybe iwth a spiraling parade of a marching band scrimshawed on it.