The Genesia was held as a public festival honoring the dead on 5 Boedromion in Athens. It is uncertain how the Genesia related to private or family rites honoring individual ancestors (held on the anniversary of the individual’s death), or to the somewhat larger-scale rites honoring the Tritopatores in Erchia and elsewhere (Parke 54) Offering was made to the Earth as well at this time (Parker, Polytheism 28).
I’ve posted my ritual for the Genesia at my other blog.
A PDF version of the ritual script is available here.
Parke, H.W. Festivals of the Athenians. Thames and Hudson: London, 1977.
Parker, Robert. Polytheism and Society at Athens. Oxford University Press: New York, 2005.