1866. Euryechimis granulatus, Terrill, Proceed. Boston Soo. Nat. Hist. vol. x. pp. 340, 352.
1868. Toxopneustes pictus, Norman, Beport Brit. Assoc. Adv. Sd. 1868, p. 314.
1871. Toxopneustes pallidus, G. 0 . Sars, Vidensk. Selsk. Forhandl., Nye Eohinodermer, p. 25.
1871. Toxopneustes dröbachiensis, Loven, Ofvers. K. Yet.-Akad. EörhandL 1871, no. 8.
1872. Strongylocentrotus dröbachiensis, A. Agassiz, Revision-of the Echini, pp. 162, 277.
1877. Strongylocentrotus dröbachiensis, Marenzeller, Ccelent. Eohin. u. Würmer d. öst.-ung. Nordpol-
Exped. pp. 3, 29 (Denksoh. d. k. Akad. d. Wissensch. Wien, Bd. xxxv.).
Test depressed, the height being proportional to the diameter as 1 :2 approximately.
Ambital outline almost circular, and only slightly subpentagonal; contour of
the profile somewhat conoid, rounded at the apex. Test well rounded beneath, and
incurved towards the interior at the margin of the actinostome. Actinostome large,
and occupying three eighths or more of the diameter. Branchial notches veiy slight.
Buccal membrane thin, and with comparatively few small, granulated, oblong scales
and ten large buccal plates. Coronal plates comparatively high, each bearing one
large primary tubercle, imperforate and uncrenulate. The series of these tubercles form
two prominent vertical lines, which extend from the apex to the actinostome, both in
the ambulacral and in the interambulacral areas. In the interambulacral areas the
plates above the ambitus bear a number of miliary tubercles, which are disposed in an
irregular manner around the primary tubercle, and form not unfrequently in small specimens
a more or less clearly defined scrobicular ring; below the ambitus a secondary
tubercle is present on each side of the primary, and, in fair-sized specimens of the
Echinus, the external ones (which stand nearest to the poriferous zone) may be traced
upon the abactinal surface of the test, extending in very rapidly diminishing series for
some distance above the ambitus. In the ambulacral areas there is a small secondary
tubercle on each plate on the inner side of the primary tubercle, the series diminishing in
size as they approach the apex, in the neighbourhood of which the secondary tubercles
become altogether undistinguishable from the few other miliaries which are present
on the plate. Near the ambitus the miliaries are fairly numerous and irregular in size,
the most conspicuous amongst them frequently forming, on the pore side of the plate,
an arched row of three or four, which stands between the arc of pores and the tubercle,
the adoral miliaries being largest. The pores are arranged in arcs of 5—6, those above
the ambitus diverging only slightly from the vertical. The apical system is large,
and also the anal ring, into which two ocular plates enter. The madreporiform and its
companion anterior genital plate considerably exceed the other genital plates in size,
which are often not much larger than the two entering ocular plates. The genital
foramina are large. The spines are comparatively fine and delicate, and vary considerably
in length, which ranges from 8 to 13 millims.
Colour.—The colour of the test is a varying shade of purplish brown, that of the
spines greenish grey, the test being sometimes green in tint also.
Size.—The northern specimens are comparatively smaller than individuals from a
more southern habitat. The largest example obtained during Sir George Nares’s expedition
was taken at Cape Napoleon, and measures 43 millims. in diameter, 21 millims.
in height, and has 20 primary interambulacral tubercles.
The following are the measurements in millims. of
A, a specimen from Discovery Bay;
B, a specimen from the Drobach Fjord.
Diameter, Height. Anal system, Actinostome. Interamb. tubercles.
A . . 39 20 6 15-5 17
B . . 42 19 5 15-1 15
Variations.—Owing to the extensive range of this boreal Echinoid, the variations
to which it is subject are so great that there are perhaps few other species which
include in their list of synonyma so large a number of specific determinations. This
arises from the fact that distant observers, depending too confidently upon the stability
of “ local forms,” have founded upon these characters numerous so-called new species,
all of which, however, have hitherto proved untenable when comparison has come to
be made with a large series of specimens.
Thus a range of examples of the northern varieties, known as 8. granulatus (Say),
Gould, and S. chlorocentrotus, Brandt, fail to present any characters of sufficient
importance to warrant their separation from the drobachiensis group, although, when
isolated and extreme examples are compared, the differences at first sight appear very
marked.
When compared with what may be called a typical specimen, the test of the
Arctic forms of 8. drobachiensis is relatively high, with the contour slightly more arched,
and having a larger actinostome and apical disk. The greatest superficial difference,
however, is presented by the spinulation. In some forms the spines of the abactinal
surface are so small and delicate, and so widely spaced, that the Echinus has almost a
naked appearance when placed beside others which are more uniformly clothed ; and it
will hardly be necessary to add that a corresponding modification exists in the size and
uniformity of the tubercles upon which the spines are borne. The more densely-spined
and more uniformly tuberculated urchin represents well the form known as granulatus;
and a glance at two such extreme individuals as those just indicated will easily account
for much of the confusion which has arisen in this species.
Both of these forms (the uniformly and the sparsely spined) occur together at
several stations in Smith Sound, and extend even to Discovery Bay. At present we
are unable to offer any definite explanation of the difference: possibly the variation
may be due to stunted growth; or perhaps it may indicate a sexual character.
Distribution.
a. Northward up Smith Sound: Discovery Bay, lat. 81° 41' N., 15-20 fms., muddy
bottom (Wares's Deeped.), the most northern locality on record; Richardson Bay, 70 fms.;
Franklin-Pierce Bay, 13-15 fms., stony, bottom temperature 29°*5 Fahr. ; Cape
Napoleon; Hayes Point, 35 fms., bottom temperature 290,5 Fahr. Greenland.
b. North o f American Continent: Assistance Bay (Penny's Exped.). All the east