I didn't see anything at Cuds on Coins that matches. Look through this and see if you can match the dies; not much about cuds there though. https://archive.org/details/guideusthreecent2003gifford/page/n1/mode/2up
The best I can tell from your photos; it looks to me like the coin took a hard hit on the rim (hollowed out area on the rim) thus pushing the displaced metal over the denticals. JMO, YMMV. Happy collecting!
Rim cuds seem to be common on 1865 3c, along with MPDs, RPDs, die clashes, etc. Look through auction archives and see if you can find yours. Here are a few from PCGS. I think it was the first time the mint struck the harder nickel alloy and there were a lot of problems. https://images.pcgs.com/CoinFacts/17290916_44268789_2200.jpg https://images.pcgs.com/CoinFacts/51855926_289923665_2200.jpg https://images.pcgs.com/CoinFacts/37114508_170113221_2200.jpg https://images.pcgs.com/CoinFacts/41732817_213160923_2200.jpg https://images.pcgs.com/CoinFacts/46261813_254776102_2200.jpg
Thanks for the links. I didn’t see mine but you are correct in that 1865 was the first year of nickel strikes and they did have problems.
If there is no damage on the edge, it's probably a cud. The nickel alloy that was used for the Nickel Three Cent Pieces chewed up dies like crazy because it was so hard.
The nickel three cent and the shield nickel both suffered from very short die life due to the hard nickel alloy If the three cent had the same die life as the shield nickel you could expect there to be around 800 die pairs for that year. It definitely looks to me like a rim cud. Gosh I wish I had pictures/drawings. Imagine the surface of the die, The fields of the die are flat and the highest part of the die. At the edge of the field there is a "step down". This is the area that creates the dentils. As you go further out there is another step down. This is the area that forms the top surface of the rim. Go out a little more and you reach the edge of the die where it drops straight down to form the neck of the die. Usually on a rim cud the die chips away on that second step to the die neck and the result is a raised lump on the flat surface of the rim. On this coin the section that creates the dentils between the field and the second stop down has chipped away creating a raised area on the dentils that is the same height as the rim,