Okay, so to start, these are pretty fun. They look like starfish!
A wild hennin has appeared!
I looked in Google Books for henins*, and the only references to the “triple-horned” variety seemed sketchy – meaning they didn’t have citations. it looks like the origin of this image and concept is from a variety of ladies journals from the 1880s. Yay Victorian myths about 15th century clothing.
But just in case, I reached out to a newly-minted Laurel who is known for her hats. She didn’t know of anything, nor could she find any solid research for this type of hat.
It looks like we’ll have to keep looking for ideas for 15th century Staryu cosplay.
*Google Book is a great place to start research, by the by, since it searches the full text of a book, whether you can see those scanned pages or not. It helps you refine terms and points you toward possible sources. I kind of adore it.
My hat is off to you as you continue your research into fancy headgear.