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

144 COLLECTIONS FROM MELANESIA.Arms at least six times the diameter of the disk, not diminishedin width for some distance out. Just beyond the disk there are threelarge upper and four much shorter sj^ines : the lowest, which is thesmallest, is very small ;gradually this disappears, and then thefollowing one gets smaller and smaller till it disappears. The upperspines are faintly echinulated near their tip ; the uppermost butone is generally rather the longest, but is never more than equal toabout the length of two of the upper arm-plates.The edge of the genital slit is fringed by some elongated plates;the bridge is pretty wide ; the mouth-shields are largo and stout,rather longer than broad, and have a notch in the middle of theirinner edge.The lower arm-plates have pretty even sides and are of about thesame length as breadth ; the tentacle-scale is only distinct at theproximal end of the arm. The upper arm-plates are twice as broadas long, broader along their distal than their proximal edge.General colour of disk yellowish grey, the radial shields violet, theupper arm-plates washed with slate-grey and having a faint whiteline along their middle ; the spines light-coloured, but darkertowards their tip ; the actiual surface lighter ; the mouth-shieldsprominent by their whiteness.Port Darwin.23, OpMothrix darwini.Disk somewhat pentagonal, with delicate spines on its upper surface,but the radial shields naked. Colour light jnuk, green, orlemon in places, with a few dark spots.Length of arms perhaps not more than six or seven times thediameter of the disk.The large radial shields form right-angled triangles, the perpendicularside being separated from that of its fellow by a very narrowline and by only a single row of rare spines ; a slight notch separatesthe plates at the peripheiy of the disk. The interradial spacesare about as broad as the base of the radial shields, and are richlycovered with delicate spinules, these extend on to the actinal surface,but leave a, bare band bordering the genital slits ; the bridge betweenthe slits is narrow ; mouth-shields broader than long, somewhat irregularlylozenge-shaped in form. The lower arm-plates are very regularlyarranged, and are only slightly oblong, many being almostcompletely square. The upper arm-plates are broader than long, theaboral edge three-sided, the adoral sides long, and the consequentform that of a not very regular hexagon. Four or five arm-spines,the lowest not peculiarly short, and the uppermost equal to fiveupper arm-x)lates in length, echinulated at their free end. Thereappear to be two very small tentacle-scales.The larger of the two specimens presents the following markings :—There are three black dots on each of the mouth-shields ; some ofthe lower arm-plates are light green, the adoral edges of others aremarked by a black spot, and this is rendered the more conspicuous