49 THE CONSTITUTION OF THE GASTROPOD PROTO-CONCH: ITS VALUE AS A TAXONOMIC FEATURE AND THE SIGNIFICANCE OF SOME OF ITS FORMS.* By H. LaiGHTON Kkstkven, D.Sc, Lecturer in Physiology AND Biochemistry, Technical College, Sydney. (Communicated hy Dr. H. G. Chapman.) (Plate i.) Introduction. In August, 1905, I read, before this Society, a paper on "The Onotogenetic Stages represented by the Gastropod Pro-toconch" (30). The more important portion of this papei had been forwarded to the editors of the Quarterly Journal of Microsco'plnd Science about six months previously, and was published in that journal in October of the same year (32). Since penning those papers — which were themselves the outcome of over four years' stud}'^ of the Gastropod Proto-conch, as represented in a collection, such as falls to the good fortune of but few to study — I have subjected the tlieories and opinions therein put forward to thoughtful criticism from time to time, and have collected further notes on the subject. Our knowledge of the Protoconch has also been enriched in the interval by many contributors, taxonomists describing new species, and my own contributions have aroused criticism, favourable and otherwise. These contri-butions, and my own recent studies in comparative Zoo-logy and Physiology, permit me to review the subject from a broader standpoint, and at the same time to treat some of its aspects in more detail. Meanwhile, during the five years which I have devoted to these other subjects, I have to a cer-tain extent lost touch with general Malacology, and must on *Submitted as a Thesis for the degree of D.Sc, to the Faculty of Science of the University of Sydney, in 19U.