Between the tentacle-scales of these first five or six tentacles and the generative slit,
there are occasionally one or two spinules.
Towards the mid arm, the side arm-plates are tumid at the sides, nearly flat below,
broader than long, and shortest where they are joined longitudinally. They have a
sharp bend to reach the side of the arm, and terminate above in an angular edge by
joining the outer edges of two upper arm-plates. Their distal margin, at the side of the
arm, is thick, and supports two very small, distant, irregular, sharp, short spines and
two tentacle-scales, the inner of which is small and scale-like; and the outer is usually,
but not invariably, a minute spine longer than the scale and the other spines. Sometimes
the two tentacle-scales are equal; ‘ and further out the largest spine becomes
independent of the tentacle. There are often no spines, while some plates have several
very minute ones. All are very ill-developed and small.
The side arm-plates form the bulk of the tip of the arm ; but, although convex at
the sides and swollen above, they do not separate the small and somewhat elongated
hexagonal upper arm-plates there.
The upper arm-plates, within the notch in the disk, are four in number, and are
broad, short, and curved to form a convex roof-like surface. Until far out on the arm,
all are much broader than long, and have slanting straight sides and very faintly curved
distal and proximal margins; the plates are convex and angular longitudinally, and they
form the upper and much of the side arm. A little beyond the mid arm, the upper arm-
plates are smaller, not much broader than long, broadest without, where they are curved ;
and further out they are longer than broad, narrow proximally, with sides reenteringly
curved and the distal margin boldly curved without. Towards the tip the elongated
hexagonal form is assumed, the distal edge, however, being curved irregularly.
Remarks.—Two specimens of this fine Ophiuroid were collected by Mr. H art: one
is in spirit, and the other is dry, in the British Museum; and they both have the same
anatomical details.
The minutely scaled disk, the widely separated radial shields and their free aboral
edge, the position and ornamentation of the generative slit, the presence of mouth- and
tooth-papillae, the absence of true teeth in the ordinary sense, the papillose nature of
the jaws, the accessory scales to the tentacular openings, the shape of the lower arm-
plates, the numerous tentacle-scales and few spines on the side arm-plates, and the
angular roof-shaped upper arm-plates, whilst they partly suggest Amphiuran and Ophio-
glyphan affinities as a whole, are very characteristic. The absence of spined generative
and radial scales, and the presence of tooth-papillae, separate the new forms from Ophio-
glypha; and the nature of the dental apparatus and tentacle-scales prevents their being
placed in any hitherto known arctic genus, except Ophiopleura.
The specimens were dredged in Discovery Bay at a depth of 25 fathoms, the
temperature being 290,5. The species has since been found in high latitudes on the
eastern side of Greenland.
Ophiopleura borealis, Danielssen & Koren, was not found very far north, and only
in latitude 63° 5' N., and to the east of Greenland; but the specimens were from
considerable depths, 510 to 570 fathoms, and the bottom temperature was above
freezing-point, l 0,3 Centigrade. I t is distinguished from Ophiopleura arctica by the
presence of 10 very definite rib-like elevations of the upper surface of the disk, and by
its large disk-scaling, and general greater robustness and dimensions of the whole body.
The species Ophiopleura arctica has a more pentagonal outline; the upper arm-plates
are more convex and medianly more pointed; and in shape the second and third
lower arm-plates differ entirely from those of Ophiopleura borealis. The other lower
arm-plates of this last species have the breadth, but the few within the disk have not the
aboral point of the arctic form. The jaws differ in shapeJ the accessory pieces are
not seen in Ophiopleura borealis. And its tentacle-scales are differently arranged and
are more numerous in mid arm than in Ophiopleura arctica. The arctic forms have
round tentacle-spaces, and the others have them elongate, at the root of the arms.
The mass of tentacle-scales and accessory pieces at their base, in relation to the
tentacle at the side of the first lower arm-plate, are very strongly marked in the form
from Smith’s Sound, but not so in that described from the sea to the east of Greenland.
Both are very fine forms and large; and the slight increase of dimensions in the boreal
type is not sufficient to explain the structural differences.
In estimating the importance of the remarkable condition of the true teeth in
Ophiopleura arctica it is necessary to remember the great variations of the teeth of
such a form as Ophioglypha texturata, Lamarck, sp. Hardly any specimens of this
species can be found with entire teeth, so constantly are they divided and conical.
The same remark holds good for Ophioglypha Sarsii, Liitken, sp.
Description o f the Illustrations o f this Species on Plate IV.
Fig. 1. The upper part of the disk and arms: natural size.
2. The under surface of the disk: magnified.
2 a. The teeth, on the jaw-plate, oblique view : magnified.
2 b. The teeth from above: magnified.
2 c. The teeth approaching: magnified.
Genus OPHIOGLYPHA, Lyman.
Ophioglypha, Lyman, Proc. Post. Soo. N .H . vii. 1860.
Ophiura, Forbes.
Disk covered with unequal, crowded, naked, more or less distorted scales, some of
which are swollen. Radial shields naked and swollen. Teeth: no tooth-papillae.
Mouth-papillae long within, but small and short near the outer edge of the mouth-
tentacles. Arm-spines few, arranged along the outer edge of the side arm-plates.
Tentacle-scales numerous; the innermost pair of tentacle-pores shaped like slits,
surrounded by numerous scales, and opening diagonally into the mouth-slits. Side
arm-plates meeting nearly or quite below, but not above. A notch edged with
papillae over the arm in the disk. The genital slits starting from the mouth-shields.
i 2