The present paper is in continuation of two parts already published under the same title and completes the Nereidiformia. Parts I and II were published in these PROCEEDINGS
for June, 1909, and April, 1910, respectively. A fourth part dealing with the remaining Polychaeta and completing the report is nearly ready for publication. The large number of species that it has been necessary to name and describe in this paper further illustrates the richness of the Polychaete fauna of California and particularly of Monterey Bay and emphasizes the incompleteness of our knowledge of the subject.