66 ON THE ECHINODERMATA OF THE
often large near the mouth-shields; and the junction of the two kinds of scaling at the
margin is sharp.
A row of spinules is often (but not always) seen along the generative slit, and is
continuous with that seen above the arm.
The mouth-shields are distant from the edge, and are boldly curved and almost
circular, except orally, where they are produced into an angle; and there are many
variations of this shape. The side mouth-shields are small, swollen and enlarged
where they impinge against the first side arm-plate; and they end between the first two
tentacle-openings visible under the arm. They are united orally in some instances.; but
as a rule the union is not perfect; and each carries a broad short scale which protects
the large first arm-tentacle, and which may be divided into two or even three parts.
The jaws are often slightly separated in front of the side arm-plates; and they are
swollen just within the large and often triangular-looking jaw-plate. ■ There are four
or five mouth-papillae on each jaw-margin, the aboral being broad and short, and the
others more or less spiniform or spear-headed. A large papilla is below the true
teeth on each jaw-angle; and it and one on either side are to be seen on the jaw-
plate.
The tentacular openings are very large ; and the first under the arm opens, as it
were, along the side of the jaw. The tentacle-scales are few, and like broad plates—
there being not often more than two on the side arm-plate, and two or three on the
side mouth-shield.
The special characters of Ophiocten sericeum, as given by Lyman, are:—“ Arms three
to four times the length of the diameter of the disk; two upper spines much the
longest; papillae of arm evenly continuous, 1-4 upper arm-plates bearing papillae.”
The main variation which we have noted in the Arctic specimens of this species
consists in the greater length of the arm-spines as compared with those of more southern
examples. In a specimen 9*2 millims. in disk-diameter the length of the upper arm-
spine of the sixth joint was 1*85 millim. (in one case 2*3 millims.); in another, with a
diameter of disk of 8*5 millims., the same spine was 1*8 millim. long, three arm-joints
in this individual being exactly 2 millims. In addition to the above, variations occur in
the contour of the mouth-shields; and in the larger examples considerable irregularity
is also found in the number and position of the mouth-papillae. Amongst this collection
are several specimens having a very decidedly pentagonal form of disk. In our opinion
none of the above variations can be regarded as of greater morphological significance
than growth-phases, or, at most, than individual variations. The largest specimen
obtained was 11 millims. in disk-diameter.
Numerous specimens were collected by both of the naturalists of the Arctic
Expedition; and one set was collected by Capt. Feilden in Discovery Bay, 25 fms., hard
bottom, Cape Frazer, 80 fms., and Hayes Point, 35 fms., bottom temperature 290,5.
The others were in Mr. Hart’s collection, from Discovery Bay, 15-20 fms., muddy
bottom, also at 11 fms.; Franklin-Pierce Bay, 13-15 fms.
ARCTIC SEA TO THE WEST OF GREENLAND. 67
Description o f the Illustrations o f this Species on Plate IV.
Fig. 8. The upper surface: slightly magnified.
9. The scaling of the upper part of the disk and part of the arm : magnified.
10. Part of the underpart of the disk: magnified.
14. Part of the disk-scaling: magnified.
Genus AMPHIURA, Forbes.
Amphiwra, Forbes, Linn. Trans, vol. xix . 1842.
Disk small and delicate, covered with naked overlapping scales, and furnished with
uncovered radial shields. Teeth: no tooth-papillee; six (rarely eight) mouth-papillae
to each angle of the mouth. Arms slender, even, more or less flattened. Arm-spines
short and regular along the sides of the arm-plates. Two genital slits.
A m ph iu r a H olbcelli, Lutken. Plate IY, Figs. 15-17,
Amphiura Holbcelli, Liitken, Vid. Medd., Nov. 1854, p. 98.
The mouth-papillae are six to each angle of the mouth (the two innermost stoutest
and pointing to the centre of the mouth), and are oblong and running upwards towards
the teeth. The innermost papilla is attached to the side mouth-shield; it is small, flat,
with a curved cutting-edge, and is long and sharp like a canine tooth. Teeth four:
two uppermost large, flat, longer than broad, squarish, rather thick, presenting a broad
free surface. Mouth-shields rounded, truncated, and narrower without; and madreporic
shield the largest, and with pores on its edge. Side mouth-shields large, broad, and
triangular, with all their sides reenteringly curved, meeting within, and also their
neighbours, between the first and second under arm-plates.
Only a single specimen of Amphiura was taken in high latitudes; and this, although
it differs slightly from the type form in the relative measurements of certain points of
detail, we have little hesitation in assigning to Dr. Liitken’s species, the variations, in
our opinion, not being of greater importance than such as we should regard as dependent
on locality and conditions of life.
The solitary specimen was found in Franklin-Pierce Bay in 15 fathoms, the temperature
being 290-5 Fahr., and presents the following characters:—
An Amphiura with disk lobed; radial shields long and narrow; mouth-shields
rounded; side mouth-shields large, subtriangular, with the sides reentering and angles
rounded. Three pairs of mouth-papillae, the middle ones placed higher than the others.
Under arm-plates pentagonal. One tentacle-scale, rounded. Arm-spines three or four.
The arms are less broad, and take their origin in a more deeply reentering curve of
the disk-margin; the radial shields are narrower; and the breadth of upper arm-plates,
in proportion to their length, is less than in the type forms, as the following measurements
will indicate .-—Diameter of disk 8 millims.; radial shield, length 1-3 millim.,
breadth 0-35 millim.; sixth upper arm-plate, length 0-6 millim., breadth 0-9 millim.
The spines are hollowcylinders, stout, blunt, and but slightly tapering; the upper spine on
K 2