This paper describes a new species, genus, and subfamily within the Scyphomedusae. Stellamedusa ventana is a relatively large scyphomedusa that reaches up to 9·4 cm in diameter. The medusa is rare, with only seven observations in over a decade of extensive surveys of the Monterey Bay and Sea of Cortez using remotely operated vehicles. Stellamedusa ventana continues the trend found in several other deep-sea semaeostome medusae in lacking marginal tentacles. The exumbrella and oral arms are covered with large nematocyst laden projections which are able to capture food items of various sizes in the laboratory. A large cydippid ctenophore was found in the gut of one captured specimen.