A new species of Magelona is described based on collections from off Long Island, New York that are identical to an undescribed species reported by M. L. Jones (1968) from the vicinity of Woods Hole, Massachusetts. The species is herein named (M. brachypalpata, new species) and described. The new species belongs to the ‘Magelona mirabilis group,' possessing a rounded prostomium, lacking prostomial horns, and having specialized chaetae on chaetiger nine. The new species is most similar to M. riojai and M. sacculata, both of which are here redescribed. Additionally, a dichotomous identification key to the known magelonid species of the northeastern American coast and a worldwide pictorial identification key to the ‘M. mirabilis' group of magelonids are provided.