Eumolpĭdae in Harpers Dictionary of Classical Antiquities
（Εὐμολπίδαι). The most distinguished and venerable among the priestly families in Attica, believed to be the descendants of the Thracian bard Eumolpus, the introducer of the Eleusinian mysteries into Attica (Diod. Sic.i. 29; Apollod. iii. 15.4.) The ἱεροφάντης was always a member of the family of the Eumolpidae, as Eumolpus himself was believed to have been the first hierophant (Hesych. s. v. Εὐμολπίδαι; Hist. iv. 83). For the judicial powers of the Eumolpidae, see the article Eleusinia, p. 582.
Eumolpidae in Wikipedia
The Eumolpidae (Greek: Ευμολπιδαι) were one of the sacred Eleusinian families of priests that ran the Eleusinian Mysteries during the Hellenic era. They popularized the cult and allowed many more to be initiated into the great secrets of Demeter and Persephone. The Eumolpidae were descendants of Eumolpus, one of the first priests of Demeter at Eleusis, through his second son, Herald-Keryx. Through Eumolpus, they were related to either Poseidon or Hermes. Starting about 300 BC, the state took over control of the Mysteries, specifically controlled by two families: the Eumolpidae and the Kerykes. This led to a vast increase in the number of initiates. The only requirements for membership were a lack of "blood guilt", meaning having never committed murder, and not being a barbarian (able to speak Greek). Men, women and even slaves were allowed to be initiated.