Epigram doesn't really fit with the other three, as it's not part of a book. Did you maybe mean Epilogue?

Hi gridlinton. Glad you are enjoying some of my grids. I had in mind the epigram sometimes placed at the beginning of a book or chapter (tckpublishing includes it in their article "Parts of a book"), but it may have been better to use the more precise term for a written epigram, an epigraph. Do you think I should change it?