Eulithidium is a genus of small colorful sea snails, marine gastropod mollusks in the family Phasianellidae, the pheasant shells. Several species in this genus were originally placed in the genus Eucosmia. However, the name Eucosmia was pre-occupied in zoology for a group of moths established by Stephens in 1829. The molluscan Eucosmia was therefore called Eulithidium to distinguish it from the group of Lepidoptera.