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

;478 C0LLECII0N8 FROM MELANESIA.fascicles of spicule-shafts, a ray proceeding from the head of each ofthe latter, extending along the membrane and supporting it (seefig. I") ; in some parts stout acerate spicules (No. 2) take part inthe formation of the dermal skeleton. Sarcode transparent, ofvery pale brown colour ; rendered subopaque, when seen in themass, by immense numbers of small elongate stellate spicules.Spicules :—(1) Triradiate of axis and dermal skeleton, consistingof a straight shaft and two arms, one tapering to a sharp point andboldly recurvate, the other ending abortively in a rounded extremityshortly after its origin ; the arms are set at right angles to theshaft and at angles of about 160° to each other, but lie in differentplanes. Length of shaft and long arm probably variable, and dependingon the position of the spicule ; the former attains a length of 5*5millim., the latter of 2 millim. ; diameter about '05 millim. It isthe shaft of this spicule which forms the longitudinal skeleton-bands.(2) Large acerate of dermal skeleton, slightly curved, tapering fromcentre to sharp points ; size about 1"8 by •05--075 millim. (3)Minute elongate stellate flesh-spicule, consisting of a straight oroccasionally curved or sinuous cylindrical shaft, beset with numerousirregular blunt processes, about 20 to the spicule, varying in lengthfrom -001 to -002 millim., thickness about -001 millim. ; length ofspicule about -0095 millim., thickness of shaft alone -001 millim.Crowded over all parts of the soft tissues.Hab. Port Darwin, 7-12 fms., bottom sand and mud ; TorresStraits, 10 fms., bottom sand.Of the two specimens from Port Darwin the larger is 74 millim.(3 inches) long in its present state, viz. without its original baseand with the apex somewhat abraded: it probably did not muchexceed this length when perfect ; its longest diameter (it is suboblongin transverse section) is 8 millim., its shortest 5 millim., atthe present base. The smaller specimen has the base attached, buthas lost the apex ; it is almost cylindrical, and has a diameter ofabout 3-5 millim. throughout. In the dermis of the larger specimenno acerates have been found, but in the smaller one theyappear to replace the triradiates in this place ; it is in this specimenthat an axial canal traverses the sponge. The specimen from TorresStraits is a fragment, forming the base of a specimen almostcertainly belonging to the same species, but very imperfect. Itsacerate differs from that of the typical form by having a diameter of•075 instead of Oo millim. ; the flesh-spicule shows no divergence.The species differs very markedly from Stewart's—(1) outwardly,in having the surface level instead of bearing sharp points ; (2)inwardly, in the presence of an cuvial cavity, in having tri- insteadof quadriradiate body-spicules, and in having a dermal aceratethe stellates of T. columnifera, further, are normal globostellatesand not elongate, as here ; in the general arrangement of theskeleton this species differs by possessing a number of longitudinallines, instead of the condensed central mass of that species.The species is obviously nearly related to a form named TrihradiionSchinidtii, well described and illustrated as the type of