Having recently 1) tried to bring some order into the great confusion, existing in the systematic literature on the Heteropods, and to eliminate some of the difficulties, which the investigator of this group of animals is sure to encounter with, I have been convinced, more than anybody else, that my study could have nothing but a provisional value, and that a firmer base could only be obtained by means of continued labour, and comparison of more material. For a systematic revision I have chosen the family Atlantidae. These animals with their tiny, inconspicuous shells, have received but little attention, and after Souleyet’s memorable work, more than half a century ago, only very few naturalists have dealt with the group. Among them I may name Gould, Smith, Oberwimmer, Vayssière and myself. Yet it may safely be said, that the discrimination of the species is perhaps more difficult than in any other family of the Heteropods.