A large collection of fishes from Tanzania, East Africa, includes representatives of four or five families of fishes. The majority of specimens are cichlids, with at least five species being represented, distinguished by osteological characters such as the shape of the opercular bones, frontals, and supraoccipital crest. These species are all named and described in the same genus based on shared scale and squamation characters. The site, at Mahenge in the Singida Region, was a crater lake about half a kilometer in diameter. It has been dated as Eocene, about 46 Ma, based on radiometric techniques. The cichlid species, being very closely related, may have constituted a species flock, which would indicate that cichlids had the ability to form flocks as early as the Eocene.