plica semilunaris

noun

plica semi·​lu·​na·​ris -ˌsem-i-ˌlü-ˈnar-əs 

plural plicae semilunares -(ˌ)ēz 

: the vertical fold of conjunctiva that occupies the canthus of the eye nearer the nose and is homologous to the nictitating membrane of lower animals