There was one great drawback to the decision of the commission for editing this jubilee volume in honour of Prof. Martin in the form that is here shown. It was namely impossible to call in the help of the most competent person for compiling the chapter on the mollusca. One cannot request a scientist to contribute to the celebration of his own jubilee. That I finally decided to undertake this work, that ought to have been done by Prof. Martin himself, is owing to the fact that I was in a better position to learn the opinions of Martin than any other, as keeper of the museum in which nearly all mollusca described by this still active worker are to be found. For this help, though it was given inadvertently, I wish to express my sincere thanks to my much honoured tutor.