"Lystrophis = tri-colored South American hognose snakes. They mimic milk snakes or coral snakes with their red, black, and white ringed patterns." Ahh where'd we be without wikipedia?
Seriously though they don't all look like that, so they might not be what you have in mind, but I'm going to tackle the whole genus anyway since I've seen each of these referred to as "tricolors" on occasion. Info is sparse so I really can't verify all of this 100%, especially the common names, but generally this seems to be what I'm finding. (If someone more familiar sees any mistakes, please let me know because I want to learn!)
South American Hognose group AKA False Yarara. This is the species dorbignyi, but there's four subspecies.
- Lystrophis d. dorbignyi (Often see it called Argentine or South American Hognose)
- Lystrophis d. chacoensis (Often see it called Argentine Hognose)
- Lystrophis d. orientalis (Patagonian Hognose)
- Lystrophis d. uruguayensis (Uruguayan or Uruguay Hognose)
Neotropical Hognose group
- Lystrophis nattereri (I often see this called Neotropical Hognose)
- Lystrophis histricus (I sometimes see this called Bicolor or False Coral Hognose)
(Occasionally I see the less common ones listed from what I think is their subfamily - "Xenodon dorbignyi", "Xenodon nattereri", "Xenodon histricus" etc)
Tricolor Hognose group
- Lystrophis pulcher (Tricolor or False Coral Hognose.)
- Lystrophis matogrossensis (Tricolor or Matogrossen Hognose)
- Lystrophis semicinctus (Tricolor or Ringed Hognose.)
These ones are a lot a like, to the point where I've seen several threads complaining about hybrids being created unknowingly.
While I can't personally verify these, here's a few methods I found of telling them apart. Between l.p. and l.m. - supposedly if you count their ventral scales and they have more than 147, it's a pulcher, but if it has less than 141 it's a matogrossensis. Also supposedly l.s. and l.p. look a like as hatchlings, but then pulcher will darker up with age. I think l.s. have lighter colors, but I hear true ones are very rare. There's also a scale count described here.
http://forums.kingsnake.com/viewarch...87966&key=2010
I think the ones most commonly found in the trade are Lystrophis pulcher, it's what you're going to see if you search for Tri Color Hognose and those are probably the ones you're after.
I find them for sale fairly regularly, hear they're prolific breeders, and have seen a lot of them converted onto f/t rodents. You can see some pictures here
http://www.alexhuereptiles.com/Colle...orhognose.html and here (He also usually has CBB ones available, so you might want to contact him)
http://theguardianreptiles.com/photos.php and I believe they come in a few morphs which you can see here (Also a brief list of species under articles there too)
http://www.heterodon.com/morphs&cat=3
While I love Lystrophis, I'm less interested in the common tricolors. (Nothing personal, the red/black/white bands just make me think of duller king snakes) Here's some I prefer that are often overlooked because of how little info there is on them, I'm always looking to learn more.
Maybe one'll grab you? (Not my pictures! Got them off of Google. I'm including links to the original sites.)
http://www.ib.usp.br/~crinog/pages/L...42site_JPG.htm
(great pics on this site, also of some tricolors for you)
http://www.westernhognose.com/
Neat zig zags
http://www.biodiversidade.rs.gov.br/...&id=133&tipo=1
These actually seem to share similar basic care in captivity, so they could all be doable if you liked. They're just typical hogs in that they prefer lizards/amphibians over rodents. That may be their biggest obstacle for people, but I've still seen many convert, especially pulcher and dorbignyi.
Overall I'd have to recommend Lystrophis pulcher because there's more on them and more people keeping/breeding them. Easier to find and also it's better in case you have any questions.
Well I'm sure most of this info was unnecessary, but I hope it helped you all the same~ 
Linear Mode
