the echinoid fauna from japan and adjacent regions part i

The Echinoid Fauna from Japan and Adjacent Regions
Test small, stout, thick, about 1.5 mm thick below the ambital region; nearly
circular in ambitaloutline, with somewhat depressed interradial median area aborally,
subconical in aboral surface; tumid on oral surface and concace with peristome at
the bottom. Apical system, a half part lacking, preserved part raised, particularly
pronounced in the madreporite; madreporite large, 3 mm wide and 1.5 mm long;
genital plates rather small, about 1.5 mm wide and 1 mm high; ocular plates almost
triangular in outline, not exsert in the preserved part; tuberculation on the genitalocular
ring very sparse, small secondary tubercles, one to two on each plate.
Ambulacra narrow, about 7 mm wide at the ambitus, and 2.5 mm at the peristomial
region; ambulacral plates rather high, about 3.5 mm wide and 1.5 mm high at
the ambital region, and made up of three components, aboral primary, middle demiplate
and adoral primary components; there are 24 or 25 plates in each column;
poriferous zones narrow, about one mm wide at the ambitus; pore-pairs in more or
less vertical arcs of triplets; pore-pair of middle demi-plate placed on the outermost,
and pore-pair of adoral primary component just below that of aboral primary one;
arcs gradually become more vertical series adapically and adperistomially; primary
tubercles rather small, plane and imperforate, placed centrally and somewhat
adorally; they form vertical series on either side of median line, and few small
secondary and miliary tubercles irregularly around the primary tubercles, and there
are more or less naked median spaces aborally; somewhat large secondary tubercles
form vertical series inside the primary series from below the ambital region to near
the peristomial region, but other small secondary and miliary tubercles rather few
in number.
Interambulacra broad, about 12 mm wide at the ambital region, and about 3 mm
wide at the peristomial region; interambulacral plates rather high, 6 mm wide and
2 mm high at the ambitus; each plate carries a small, plane, and imperforate primary
tubercle, being placed centrally and adorally on a plate; 19 or 20 plates in each
column; primary tubercles, which are as large as, or slightly larger than, those on
the ambulacra, form a vertical series on middle of each column; more or less large
secondary tubercles placed inside and outside, or above the primary tubercle on the
plate aborally, and other small tubercles few in number; there are distinct bare
median areas aborally; adorally, somewhat large secondary tubercles form vertical
series two outside and one inside the primary series from below the ambitus approaching
to the peristomial region, and other small secondary and miliary tubercles
very few in number; the feature of this species resembles the living Tr. gratilla in
the naked median area and in many (but fewer than in that species) vertical series
of large tubercles on the adoral surface. Peristome rather small, markedly concave
toward the peristome; gill-slits sharp, deep and broad, about 1 mm wide and 1.5 mm
in length. Auricles well developed, stout and high, two auricles contact in rectangular
form, about 3 mm high and 3 mm wide.
DistinctioJl.-This Eocene species differs from allied genera and species, e. g.,
Psammechinus hispaniae LAMBERT, 1889 (LAMBERT, 1889, p. 703.-LAMBERT, 1902, p.
37, pI. 2, figs. 16-19-Echinidae), from the Eocene of Barcelona, and Psam. biarritzensis
COTTEAU, 1863 (COTTEAU, 1863-b, p.678.-COTTEAU, 1889-94 (93), p.625, pI. 353,
figs. 1-6), from the Eocene of Biarritz (Pyrenees), by the tuberculation on the coronal
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