1876. Astrophyton Agassizii, Norman, Proc. Boy. Soc. vol. xxv. p. 208.
1877. Astrophyton Agassizii, Lyman, Proceed. Boston Soc. Nat. Hist. vol. xix. p. 102.
1877. Astrophyton arcticum, Smith, MS.
Disk with prominent radial ribs, which taper slightly towards their inner
extremities, and reach nearly to the centre,—their outer extremities forming a bold
protuberance at the margin of the disk, above the junction of the rays. The ribs
bear a number of irregularly disposed, short, conical spinelets, or spiniform tubercles.
The disk is covered with a leathery skin; and upon the interradial spaces, which are
smooth and well shield-shaped, a few granules are present. Mouth-shields either
quite insignificant or aborted. The side mouth-plates, which are large and irregularly
pyriform in outline, meet along the greater portion of their apposed sides. The jaws
(scutella oralia) are nearly as large as the side mouth-plates, subtriangular in form,
and touch along their apposed sides, except for a short distance at the aboral extremity
of the same. In spirit it is difficult and often impossible to distinguish the various
parts, in consequence of the thick investing skin. Mouth-papillae and tooth-papillae,
which are spiniform and slightly tapering, are undistinguishable in form; 6-10, which
may, by their position, be classed as the former, are disposed on the margin of the
jaw-plate, whilst an irregular group stands in the place of tooth-papillae. The
interbrachial spaces on the actinal surface contain a few calcareous plates or
scales; and at the extreme margin a closely aggregated number of these plates form
a band which divides the upper and lower surfaces of the disk. Under arm-plates
variable and divided; side arm-plates broad and band-like. The tentacle-scales, which
are spiniform and not flattened, are normally four in each series, this number being
diminished by one or two on the portion of the ray below the first forking. Rays
forked dichotomously, the portions between the forks being comparatively long and
unequal in length. Upper surface of the rays granulated, each joint being marked
off by a suture-like depression, and the granules being gathered into a saddle-like
point on the sides of each joint. A similar sutural depression or furrow traverses the
dorsal median line of the ray. Towards the extremity the granules form a regular
double series round the joint, the space between neighbouring series being several
times the breadth of the band. These granules have claw-like hooklets articulated
upon them, which are attached to a right- and left-hand knob alternately, and are
present in greatest numbers towards the terminal portion of the rays. The ray up
to the first forking has but very few granules, the stem next the disk being covered
with a thick investing membrane.
Colour.—According to Stimpson, the radial ribs are yellow, and the interbrachial
spaces brown, in the living animal. In dried examples the ribs are a yellowish brown,
the rays being somewhat lighter in shade, and the interbrachial spaces a rich dark
brown. In spirit preparations this difference is less marked, and frequently destroyed
altogether.
Remarks.*—In the preliminary Report on the Echinodermata collected during
the Arctic Expedition of 1875-6 (Ann. & Mag. Nat. Hist. ser. 4, vol. xx. p. 468), an
example belonging to this species was cited under the name of A. arcticum, Leach
the writers, as there stated, not having had at the time an opportunity of seeing the
specimen. Upon subsequent examination the Astrophyton in question, which had
been dredged off West Greenland by Mr. A. C. Homer (who accompanied Sir Allan
Young in the 4 Pandora ’), at a depth of 600 fathoms in Smith’s Sound, lat. 78° 19' N.,
long. 74° 30' W., was found to be identical with the species which had been described
by Stimpson as A. Agassizii, a form not uncommon in the Arctic Seas of Greenland
and North America. Careful and thorough search was then made for Leach’s type
specimen of Gorgonocephalus arcticus (obtained by Sir John Ross), which was
deposited in the British Museum. Prof. F. Jeffrey Bell very kindly took much trouble
on our account, and rendered every assistance in his power by carefully looking up
all the specimens in the national collection. Unfortunately it is impossible to say
with certainty that the object of our quest was found. An old dried specimen, however,
is still extant which is supposed to be Leach’s type, and which, from its fragile nature,
has never been moved since it was originally set out by him. This is at least the
traditional (!) representative of Gorgonocephalus arcticus; for it is without ticket of any
kind. Although this absolute evidence is wanting, there appears to be little doubt about
the correctness of the supposition. This old specimen would seem to be unquestionably
referable to Stimpson’s species, and also to accord most closely with the example which
forms the subject of the present remarks. If, therefore, the specimen above
mentioned be really the Gorgonocephalus arcticus of Leach, that name and Astrophyton
Agassizii of Stimpson will stand as synonymous terms.
We quote in full the original'diagnosis given by Dr. Leach; as a further evidence
in support of our views, and also as a testimony to the careful study and acumen of
Mr. Edgar A. Smith, who was the first to refer to this hitherto overlooked and almost
forgotten description:—
“ Genus G orgonocephalus, Leach (1815). Euryale, Lamarck (1816).
“ Species Arcticus. Corpore supra radiatim costato: costis tuberculatis, radiis
longissimis, tenuibus, supra granulatis; articulis (apicalibus prgesertim)
distinctissimis.” *
From the brevity and ambiguity of this description, together with the element
of uncertainty which is now inseparable from the type, and which can never be
cleared away, we do not feel justified in restoring Dr. Leach’s name in the face of the
present universal adoption of Dr. Stimpson’s ; although, if all points were equal, the
former would undoubtedly claim priority.
Distribution.
a. Northward up Smith's Sound: Lat. 78° 19' N., long. 74° 30' W., 600 fins.
* A Yoyage of Discovery in H.M.SS. ‘ Isabella ’ and * Alexander ’ for the purpose of exploring Baffin’s
Bay and enquiring into the probability of a North-west Passage.’ By John Boss (1819), Yol. ii. [Append.
No. iv. by W. E. Leach], p. 178.