Notodelphyidae and Botryllophilidae are families of cyclopoid copepods, usually associated with Tunicata. Although SARS (1921) considered the families closely related, and placed them together in his suborder Notodelphyoidea, LANG (1946) showed that this group was polyphyletic. The two families are treated here together, simply because both are associated with the same host group. Through unforeseen circumstances (loss of part of the material while sent out on loan), the publication of this paper was considerably delayed. Certain details that had to be checked, could not be verified owing to the loss of the material involved. In my opinion, however, the available data are still of sufficient interest to warrant publication.