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

—;364 COLLECTIONS FROM MELANESIA,37. Psilacal)aria gracillima.(Plate XXXVII. figs. D-D" ; Plate XXXVIII. figs./-/".)Corallum extremely delicate, erect, branching dichotomously,approximately in one plane, and at approximately right angles.Apparently no anastomosis. Internodcs 12-16 millim. long, diameter•3 to '7 millim., cylindrical, slightly flexuous. Soft joints inconspicuous,not broader than the adjacent internodes. Axis of internodeshard, white, not striated.Cortex about one quarter the thickness of the whole branch, roughenedby the large spicules. Verrucee arranged in spiral series, withbases almost in contact on larger branches, rather distant and onopposite sides on the smaller ones ; triangular and flattened in theformer, low, rounded, and tubercular in the latter ; basal diameterand height 1 millim. in the large to "5 millim. in the small branches.Colour of cortex white, of tips of verrucas pale yellow.Spicules of general (i.) cortex:— Large cylindro-fusiform to subclavate,with thick axis, slightly tapering to round-pointed ends, wellprovided with strong tubercles about '03 millim. high, either subsphericalor forming low roughened ridges often extending round asmuch as one quarter of the circumference of the spicule (appai'entlyrepresenting tubercular whorls of those spicules of other Melithseidaewhich possess them) ; size -28 to '31 by '087 millim. ; tuberclescommonly more abundant and larger near one end than the other,(ii.) Smaller, fusiform, with sharply pointed ends and prominentpointed and roughened tubercles, more or less curved, scatteredabundantly all over ; size -21 to '25 by -OoS to "071 millim. (also atbase of verrucee) [probably young forms of (i.)]. Spicules of verrucae :(iii.) Similar to (i.), but with less broad and ridge-like tubercles,measuring as much as '3 by "087 millim. ; on exterior of the verrucae,except just at the apex, (iv.) Subclavate, tapering from a broad toa sharp-pointed end, well covered with irregularly scattered, prominent,pointed tubercles, which become larger towards the broadend, where they project forwards beyond and in the direction ofthe axis of the spicule ; on the inner wall of the verrucae, thusresembling the subapical verruca-spicules of Acaharia divaricata.(v.) Smaller, fusiform, with fewer tubercles, pointed, scatteredequally all over, two or three terminal ones at one end prolongedmuch as in (iv.) ; size "21 to '25 by "035 to '044 millim. ; on apex ofverrucae [probably young forms of (iv.)]. (vi.) Intermediate formsbetween (i.) and (ii.), with tubercles more distinct and smaller thanin (i.) ; size '31 by "07 millim. ; on general body of zooid.Of all these six forms I only distinguish 3 distinct types, viz. :(i.) [including iii. and vi.] representing the large cortical fusiform ofother Mclithaeidae, but found also on the verruca, from the fact ofthe latter being covered more or less with what represents thegeneral cortex ;(ii.) representing the smaller cortical fusiform andperhaps also the horizontal verruca-spicule of other Melithoeidae(iii.) [including v.] representing the longitudinal verruca-spicule,