Genus Cepphus, commonly known as the guillemots, is a group of seabirds that belong to the family Alcidae. These birds are distinguished by their black and white plumage and unique bills that vary in shape depending on the species. There are four recognized species within the genus Cepphus: the black guillemot, pigeon guillemot, spectacled guillemot, and the long-billed murrelet. Each of these species has different characteristics that make them unique, but they are all part of the same genus. While there are no known synonyms for the term "genus Cepphus," there are various scientific and common names that describe each of the individual species.