About the word felix, I can't grasp what L&S means here :
What kind of genitive is this, grammatically ?(b). With gen. (poet. and in post-Aug. prose): “Vergilius beatus felixque gratiae,” Plin. H. N. 14 praef. § “7: o te, Bolane, cerebri Felicem!” Hor. S. 1, 9, 12: “felices studiique locique,” Ov. M. 5, 267: “felix uteri,” Sil. 4, 359: “leti,” id. 4, 398: “famae,” id. 4, 731: “felices operum dies,” Verg. G. 1, 277.—
I think I am understanding felix famae, felix uteri, dies felices operum, felix gratiae, felix loci,
but I don't understand felix leti (death), felix cerebri (anger).