144 COLLECTIONS FBOM MELANESIA. 



Arms at least six times the diameter of the disk, not diminished 

 in width for some distance out. Just beyond .the disk there are three 

 large upper and four much shorter spines : the lowest, which is the 

 smallest, is very small ; gradually this disappears, and then the 

 following one gets smaller and smaller tiU it disappears. The upper 

 spines are faintly echinulated near their tip ; the uppermost but 

 one is generally rather the longest, but is never more than equal to 

 about 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 large and stout, 

 rather longer than broad, and have a notch in the middle of their 

 inner edge. 



The lower arm-plates have pretty even sides and are of about the 

 same length as breadth ; the tentacle-scale is only distinct at the 

 proximal end of the arm. The upper arm-plates are twice as broad 

 as long, broader along their distal than their proximal edge. 



General colour of disk yellowish grey, the radial shields violet, the 

 upper arm-plates washed with slate-grey and having a faint white 

 line along their middle ; the spines light-coloured, but darker 

 towards their tip ; the actinal surface lighter ; the mouth-shields 

 prominent by their whiteness. 



Port Darwin. 



23. OpMothrix darwini. 



Disk somewhat pentagonal, with delicate spines on its upper sur- 

 face, but the radial shields naked. Colour light pink, green, or 

 lemon in places, with a few dark spots. 



Length of arms perhaps not more than six or seven times the 

 diameter of the disk. 



The large radial shields form right-angled triangles, the perpen- 

 dicular side being separated from that of its fellow by a very narrow 

 line and by only a single row of rare spines ; a slight notch sepa- 

 rates the plates at the periphery of the disk. The interradial spaces 

 are, about as broad as the base of the radial shields, and are richly 

 covered with delicate spinules, these extend on to the actinal surface, 

 but leave a bare band bordering the genital slits ; the bridge between 

 the slits is narrow ; mouth-shields broader than long, somewhat irre- 

 gularly lozenge-shaped in form. The lower arm-plates are very regu- 

 larly arranged, and are only slightly oblong, many being almost 

 completely square. The upper arm-plates are broader than Jong, the 

 aboral edge three-sided, the adoral sides long, and the consequent 

 form that of a not very regular hexagon. Four or five arm-spines, 

 the lowest not peculiarly short, and the uppermost equal to five 

 upper arm-plates in length, echinulated at their free end. There 

 appear 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 of 

 the lower arm-plates are light green, the adoral edges of others are 

 marked by a black spot, and this is rendered the more conspicuous 



