The sub-genus Perinereis, according to Grube’s views, contains all Nereis-species, characterized by having the lateral dorsal paragnathi of the basal ring of the proboscis (group VI) all or some of them transverse, ridge-shaped, the remaining paragnathi being conical, or pin-shaped (»pectiniformes” Kinberg), or compressed; the feet all of the same structure, or those of the posterior region of the body more enlarged. This division mainly corresponds to Kinberg’s family Aretidea, and not to his genus Perinereis, containing the species, which have no pectiniform teeth and but little modified posterior feet. However it seems preferable to me to maintain Kinberg’s name, as I do not like to increase the systematical literature with a new one, and because the greatest number of species of the family Aretidea are united in the genus genera Perinereis, the four other [Arete, Pseudonereis, Paranereis and Naumachius) containing only a small part of them. To use the name Lipephile, afterwards proposed by Malmgren for N. cultrifera, instead of Perinereis, as done by Claparède a. o., seems not justified to me, because the name Perinereis has the priority, and moreover the name Lipephile is applied by Claparede in a sense different from what it was intended for by its author. I prefer to base the subdivisions of the genus Nereis rather on characters taken from the arrangement of the paragnathi, than on the state of development of the dorsal lobe of the feet. The main groups of paragnathi of the proboscis are rather constant and appear not to be liable to much variation in the same species; moreover the knowledge of their arrangement enables us to recognize also the systematical position of the Heteronereis-forms. On the contrary the lobes of the feet are liable to much variation in different regions of the body, and show such marked changes in individuals coming to sexual maturity, that I do not think it advisable to rely much upon their characters for classification.