Some Opisthobranchiate Mollusca from Hawaii!

IN THE AT~EMPT to advance our knowledge of the manne Mollusca of the Hawaiian Islands, groups provided with a shell have been among the first to receive attention. Largely for this reason gastropods of the order Prosobranchiata, having conspicuous shells, have become better known than have such forms as belong in the order Opisthobranchiata in which a shell is often absent in the adult.' Such nonshelled forms present difficulty of adequate diagnosis for the establishment of taxonomi~ characters, inasmuch as the' preserved animal soon loses its colors, partly or completely, and becomes in some way distorted because of the contraction of various anatomical parts. Since the works of Gould (1852) and Harper Pease (1860-1872), nothing appears to have been added to' our knowledge of these animals in the Hawaiian area. The present work is but a small part of what needs to be done in this large group of mollusks, which is well represented in Hawaii. Only those forms whose generic position has already been established are dealt with here. No dissection has been attempted, and specific characters have been based on external features only. The colored figures, as well as