Report on the zoological collections made in the Indo-Pacific Ocean ...

608 COLLECTIONS FBOM THE WESTEKN INDIAN OCEAN.Islands give the following measurements : acuato -2 to "25 by '007millim. ; tibiella -2 to -25 by -004 millim.Hah. Mozambique ; Marie Louise Island, Amirante group ; tidemarksto 17 fms.DESMACIDINID^.The occurrence of a true Desmacidon in the Indian Ocean is perhapsfor the first time indicated by the new species described below.The two species assigned to the genus by Ehlers (' Die EsperschenSpongien') appear to belong respectively to Ampliilectus and Clatliria.The wide range possessed by species of the new genus lotrocliota isshown also by the occurrence of our two new Australian species,one of them being abundant in both localities.RHIZOCHALINA.The scarcity of this genus, so common in the tropical waters ofAustralia, and well represented also in the south of that continent,is probably due to the absence of mud from the localities investigated; slightly deeper dredging, clear of the reefs, might be expectedto reveal more of this interesting genus, which had nothitherto been noted from any localities nearer than Ceylon (Carter,Ann. & Mag. N. H. 1880, vi. p. 37, under the name of Desmacidonjeffreysi).29. EMzochalina pellucida. (Plate LIV. fig. j.)Elongate, tapering gradually from base of sponge to summit offistula. Fistula single, straight. Surface even, glabrous. Consistencein spirit soft, brittle ;colour very pale brown ; appearancesemitransparent. Body of sponge oval, compressed ; includes foreignbodies.Main skeleton a somewhat confused mass of moderately closelyfelted and irregularly crossing spicules, traversed at intervals bytracts of compact spiculo-fibre, 4-8 spicules broad, running parallelto the surface. Dermal skeleton consisting of long, straight, compactspiculo-fibres, 4-20 spicules broad, branching at acute angles, andthus spreading over the surface ; the intervals occupied by a looseopen reticulation of single spicules or of fascicles two or three spiculesbroad, crossing at various angles. Sarcode pale yellowish brown,subtransparent. Spicule accrate, slightly curved, tapering graduallyto sharp points from about middle of spicule ; size '26 by -01 millim.Hab. Providence Island, Mascarene group, 19 fms, ; bottom coral.A single specimen, 87 millim. (3| inches) long, 12 miUim. ingreatest basal diameter ;greatest diameter of present end of fistula3 millim.In its svibtranspareucy, and in the great thinness of the dermallayer of the skeleton, as well as in its having been apparently sessileby a bulbous base, this differs from all described species of thegenus.