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Show 440 PROF. J. A. THOMSON AND MR. W. D. HENDERSON ON [Apr. 10, The stalk is uncoloured and covered by irregular longitudinal ridges. There is evidence of a slight basal expansion, but this may be partly due to a contraction of the basal coenenchyma, through which the end of the axis has been thrust. There is a slight swelling at the top of the stalk. The central axis (almost 1 m m . in diameter) tapers markedly for the last 4 millims., and ends in a twisted coil. The metarachidial surface shows (1) an almost bare streak about 1*75 m m . in breadth, with a few (seven) zooids in a single row towards the upper end ; (2) a deep median furrow which is evaginated as a ridge towards the base, doubtless a post-mortem result; (3) fine, close-set, longitudinal striations, about 12 on each side of the middle line; (4) scattered superficial spicules. The median zooids have a diameter of about 0*25 mm., and show no trace of tentacles. The prorachidial surface has a bare space about 2 millims. in diameter; it shows a deep median groove, longitudinal striations less marked than on the other side, and a few irregularly-scattered spicules. The end of the prorachidial insertion of the pinnule is almost on a level with the metarachidial insertion. The zooids occur on the inferior surface of the pinnules, and their insertion is what is termed median. Beginning with a cluster at the prorachidial insertion of the pinnule, they rise in a narrow crescent away from the base and descend gradually to the metarachidial insertion. They are white in colour and stand out like little octoradiate stars. This species falls into Kolliker's second section with median zooid-plates and into the group Pt. pellucidum. It comes nearest Pt. gracile, but differs from it in many features, e. g. in having four main rays instead of 7-9, in having one row of marginal polyps instead of two, in having a very short zooid streak instead of a very long one (25 millims.). Locality. Wasin Channel, 10 fathoms. LITERATURE REFERRED TO. 1900. ASHWORTH, J. H.-"The Xeniida?." Willey's Zoological Results, part iv. 1834. EHRENBERG, C. G.-Die Corallenthiere des Rothen Meeres. 1870. GRAY, J. E.-Catalogue of the Lithophytes or Stony Corals in the British Museum. 1887. GRIEG, J. A.-" Bidrag til de Norske Alcyonarier," in Ber-gens Museum Aarsberetning. HERKLOTS, J. A.-Notices : Polypiers nageurs on Penna-tulides. 1894. HICKSON, S. J.-" A Review of the Genera of the Alcyonaria Stolonifera." Trans. Zool. Soc. London, vol. xiii. 1900. Ibid.-" The Alcyonaria and Hydrocorallina? of the Cape oi Good Hope." Marine Investigations in South Africa. vol. i. |