the echinoid fauna from japan and adjacent regions part i

200 S. NISIYAMA
There are two relatively well preserved specimens of this new species at the
writer's disposal.
Test finely arched with somewhat roundly pentagonal ambitus, slightly concave
orally, peristome deeply sunken adorally; 15 interambulacral plates in each column
and with about 17 ambulacral plates corresponding them. Apical system wanting,
the vacant space of moderate size, about 4 mm across.
Dimensions of Halatype.-26 mm in horizontal diameter, and 18 mm in height.
Ambulacra slightly curved, broad at the ambitus and near the peristome, more
or less petaloid orally; poriferous zones narrow, 1.5 mm wide at the ambital region,
narrow adapically and broad adorally; ambulacra remarkable for the excessive development
of certain primary tubercles. Ambulacral plates obviously made up of
three components, median primary component with smaller (demi-plate components)
adorally and aborally, crowded, apparently make a triserial row below the ambitus;
but every fourth plate typically greatly enlarged at its innerside and shut out the
three succeeding plates from the median line with introducing a small secondary
tubercle nearly throughout. So far as known this structure of ambulacral plates
does not occur elsewhere among the Echinoids, except for the living St. varialaris
(LAMARCK, 1816), the type-species. Interporiferous areas with two prominent vertical
series of large, imperforate, non-crenulate, primary tubercles besides several series
of secondary tubercles and miliaries, some entering the poriferous zones, diminish
at the peristomial edge, where the areas narrow; about 4 mm wide, over twice of
the poriferous zones at the ambitus.
Interambulacra with a linearly undulating groove in each median area, broad
above the ambitus, narrow near the peristomial region, with principal vertical series
of primary tubercles resembling those of the ambulacra in feature, but decidedly
larger, diminishing in size adorally Two series of large secondary tubercles on
both sides of the primary series, smallest orally, which reach some distance above
the ambitus, with small secondary and miliary tubercles irregularly distributed.
Seen from aboral side, twenty radiating series of primary tubercles, two series in
each area; of rather equal size and decidedly larger than the numerous accompanying
secondaries.
Peristome small, only 6 mm in diameter, subpentagonal in outline, decidedly
concave orally, rather indented by wide, well-developed gill-slits. There are several
(3-5) papillae (attachment of sphaeridia) on the oral part of each ambulacrum; each
is attached to a miliary tubercle (papilla), but is not associated with any depression
Qr other shelter. Spines not accessible.
This new species undoubtedly belongs to an interesting and characteristic genus
Stamapneustes AGASSIZ, 1841, on account of the character of the ambulacral structure
of the ambulacral plates and a linearly undulating groove in each median area of
the interambulacra; however, the writer is not accessible to the auricles. After
careful examination of the living St. varialaris (PI. 4, fis. 1-2), the writer feels justified
in adhering to the present determination, too.
Distinctian.-This new species closely resembles St. varialaris (LAMARCK, 1816) (o-p.
cit.), the living species of the Indo-West Pacific Oceans, but the larger number of the
coronal plates are easily distinguish this species from the latter; for example, in