There is still often confusion as to the identity of species of compound ascidians. This is due sometimes to a lack of published observations on the group, and sometimes to seasonal variations from the described condition. An attempt has been made to follow the growth and variation of the species in the Plymouth area throughout the year. During the course of these investigations all the species of the sub-order Aplousobranchia formerly recorded from this area were encountered, with the one exception of Distaplia garstangi Berrill. In addition, two new species were taken: a species of Polycitor, the first record of the genus in these waters, and a species of Lissoclinum.