No. 7. — Notes on some Australian and Indo-Pacific Echino-derms. By Hubert Lyman Clark. The Trustees of the Australian Museum having placed in my hands the collection of echinoderms made by the "Thetis" in 1898, it has seemed desirable before studying that collection to work over the Aus-tralian material in the M. C. Z. collections and to describe the new forms. I have to thank Mr. Robert Etheridge, Curator of the Museum, for his courteous approval of this plan. I have found that the ophiurans of the genera Pectinura and Ophiopeza offer some peculiar difficulties and it has been necessary to make a very careful study of those genera and their allies. This has led to a complete revision of all the known species of ophiurans of that group (which may be styled Ophiarachna sensu Muller and Troschel -+• Ophiopeza sensu Peters), and I incorporate my results in this paper. ASTEROIDEA. ASTROPECTINIDAE. Astropecten. The M. C. Z. collection contains half a dozen Astropectens from the coast of New South Wales. Two of these are without doubt A. polyacanthus M. and T., but the other four are less easy to determine. One was received in exchange from the United States National Museum and is labelled " Astropecten triseria-tus M. & T., Botany Bay, Australia." The other three are undoubtedly the same species and are so labelled, but were received from the Australian Museum, and were collected off Port Jackson. These specimens agree well with Miiller's and Troschel's description of A. triseriatus, except in the most important point. The large spines on the supramarginal plates are in a single series and there is no trace of the second and third series, characteristic of Muller's and Troschel's species, except that on a very few plates a second small spine is present close beside the principal one. I see no reason to doubt that this is the A. triseriatus of Whitelegge's list (Journ. Roy. Soc. N. S. W., 23, p. 200), but that it is the A. triseriatus of Muller and Troschel seems to me very doubtful. Except for the fact that the ventral and marginal spines are strongly flattened instead of being cylindrical, I should have no hesitation in referring these specimens to Sladen's A. acanthifer from the Banda Sea, but the difference in the spines is so marked I hardly think such identification would be correct.