'Alert' 1881-2

ECHTNODERMATA. 135
Diameter of disk 19 millim., length of arm about 83 millim. from
the edge of the disk, width of arm at disk 6 millim., height of same
5 millim. Fourteen mouth-papillse of fair size, the outermost the
largest ; four stout teeth ; mouth-plates with six sides, the ahoral
the longest and the adoral the shortest, longest hardly longer than
broadest axis ; accessory mouth-plates large, longer than broad,
straight within, convex without; side mouth-shields distinct, inclined
to be triangular, broader within than without ; granulated
space between mouth-papillaj and mouth-shield very small.
Lower arm-plates at first wider than long, but varying a good
proceeding outwards the adoral edge becomes shorter
deal in shape ;
and shorter as the side arm-plates encroach more and more upon the
ventral middle line. The upper arm-plates at the base of the arms
are very wide, about foui* times as wide as they are long, further
out they become narrower, and towards the tip of the arm are very
much encroached upon by the side plates ; as a rule there are seven
spines ou the plates. Tentacle-scales two.
This fine form stands nearest to P. marmorata, from which it
may be distinguished by (i.) the much larger radial shields, (ii.) the
wider arm-bases, (iii.) smaller number of arm-spines, (iv.) larger
accessory mouth-shield, and (v.) proportionately shorter
Port Molle (14 fms.).
arms.
OPHIOPINAX, g. n.
It appears to be necessary to establish a new genus for the re-
ception of the form hitherto known as Pectinura steUata, owing to
the remarkable and regular arrangement of the large plates on its
disk ; this, which is only obscurely seen in smaller specimens, becomes
very prominent in such larger examples as were obtained
during 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 shields
large, separated by several radial or interradial plates from one
another. All the disk, except the radial shields, is covered by
granules, but there are no spines or spinous processes. Teeth (in
four rows) stout, blunt. Side arm-plates extend on to both actinal
and abactinal surfaces ; side mouth-shields naked.
The extraordinary development of the plates between the radial
shields, both of the same and of the neighbouring sets, appears to
have escaped the notice of Ljungman and Grube ; nor can it, I
imagine, have been noticed by Mr, Lyman, as he retains 0. stellata
of Ljungman in the emended genus Pectinura.
At this time it ajjpcars convenient to redescribe and figure the
species.