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

ECHTNODERMATA. 135Diameter of disk 19 millim., length of arm about 83 millim. fromthe edge of the disk, width of arm at disk 6 millim., height of same5 millim. Fourteen mouth-papillse of fair size, the outermost thelargest ; four stout teeth ; mouth-plates with six sides, the ahoralthe longest and the adoral the shortest, longest hardly longer thanbroadest axis ; accessory mouth-plates large, longer than broad,straight within, convex without; side mouth-shields distinct, inclinedto be triangular, broader within than without ;granulatedspace between mouth-papillaj and mouth-shield very small.Lower arm-plates at first wider than long, but varying a gooddeal in shape ;proceeding outwards the adoral edge becomes shorterand shorter as the side arm-plates encroach more and more upon theventral middle line. The upper arm-plates at the base of the armsare very wide, about foui* times as wide as they are long, furtherout they become narrower, and towards the tip of the arm are verymuch encroached upon by the side plates ; as a rule there are sevenspines ou the plates. Tentacle-scales two.This fine form stands nearest to P. marmorata, from which itmay be distinguished by (i.) the much larger radial shields, (ii.) thewider arm-bases, (iii.) smaller number of arm-spines, (iv.) largeraccessory mouth-shield, and (v.) proportionately shorter arms.Port Molle (14 fms.).OPHIOPINAX, g. n.It appears to be necessary to establish a new genus for the receptionof the form hitherto known as Pectinura steUata, owing tothe remarkable and regular arrangement of thelarge plates on itsdisk ; this, which is only obscurely seen in smaller specimens, becomesvery prominent in such larger examples as were obtainedduring the voyage of the ' Alert.'The genus may be defined as follows:—Two elongated genital clefts;mouth-papillse, teeth. Accessory oral shields ; arm-sijines delicate,attached to the outer edge of the side arm-plates. Eadial shieldslarge, separated by several radial or interradial plates from oneanother. All the disk, except the radial shields, is covered bygranules, but there are no spines or spinous processes. Teeth (infour rows) stout, blunt. Side arm-plates extend on to both actinaland abactinal surfaces ; side mouth-shields naked.The extraordinary development of the plates between the radialshields, both of the same and of the neighbouring sets, appears tohave escaped the notice of Ljungman and Grube ; nor can it, Iimagine, have been noticed by Mr, Lyman, as he retains 0. stellataof Ljungman in the emended genus Pectinura.At this time it ajjpcars convenient to redescribe and figure thespecies.