the echinoid fauna from japan and adjacent regions part i

The Echinoid Fauna from Japan and Adjacent Regions
Japan.
There is a fossil subspecies from Central Japan at the writer's disposal and
described herein.
Stereocidaris grandis jusana NISIY AMA, n. subsp.
(PI. 1, fig. 4)
Compared with:
Dorocidaris grandis DODERLEIN, 1885, p. 77.-Stereocidaris grandis (DODERLEIi\:) DODERLEI:-':,
1887, p. 3, pI. 1, figs. 1-6, pI. 2, figs. 1-11, pI. 8, figs. 2a·m.-A. AGASSIZ and H. L. CLARK,
1907, p. 22, pI. 5, figs. 18-20 (partim, pI. 36, St. grandis hyatorina MORTEi\:SEJ':, 1928,
non pI. 33) .-H. L. CLARK, 1925, p. 26 (partim ; Challenger St. 210,= St. indica Philippinensis
MORTENSEN, 1928).-MoRTENSEi\:, 1927, p. 299.-MoRTENSEN, 1928-b, p. 233, pI. 18, figs.
4-6, pI. 19, figs. 1-3, pI. 70, figs. 1-2, pI. 80, fig. 35.-Stereocidaris microtuberculata H. L.
CLARK, 1907, p. 220, pis. 1-2 (non YOSHIWARA, 1898).
Holotype.-IGPS colI. cat. no. 73741.
Locality and geological horizon.-IGPS loco no.-Ch-12.-Tuffaceous sandstone of sea
c1.ff below shrine at T6miya, Takeoka-mura, Kimitsu·gun, Chiba Prefecture. (tm
Futtu, Lat. 35°12'52/1N., Long. 139°51'E.), Kurotaki formation (T6miya tuffaceous sandstone),
Lower Pliocene. (Collected by K. HATAI, S. NISIYAMA, T. KOTAKA, and K.
HATORI, 1950).
There is only a part of corona of this subspecies at the writer'S disposal: it is
finely preserved, and well shows its subspecific characters.
Coronal plates rather thick, about 1 mm in upper coronal plate. Ambulacra distinctly
sinuate; interporiferous area much broader than a poriferous one, about three
times as broad as the poriferous area; marginal series of tubercles very regular, and
the tubercles somewhat contiguous; inside the marginal tubercles, each plate carries
a secondary tubercle nearly as large as, or somewhat smaller than those of marginal
one adapically and adorally, or large secondary tubercles accompanying a small
tubercle below the secondary one; farther inside of the secondary tubercle, each plate
carries usually two small tubercles, about a half in size of large secondary tubercle,
situated at upper and lower corners of the plate; these large secondary tubercles
and small tubercles form four of very regular longitudinal series within the series of
marginal tubercles, and the whole interporiferous area so narrow that it is quite filled
up by those six series, no naked median space being left. Poriferous area narrow,
about 1 mm wide at the broadest point, somewhat depressed; pores about equal in
size, and separated by a more or less broad, slightly elevated wall, whereas the ridge
separating pore· pairs is rather high, pores being fairly deep lying.
In interambulacra, areoles fairly deep and well separated, those on oral side
slightly transverse-oval; the uppermost areole rudimentary and without a primary
spine, as is usual in the Stereocidaris; but areole and its tubercle not so very small,
about 1.5 mm wide and 2 mm high in a plate about 6 mm wide and 5 mm high;
scrobicular ring very regular, rather conspicuous, and somewhat raised, the tubercles
being more than twice as large as the marginal ambulacral ones, almost contiguous,
number of tubercles in a ring being 14-16; ring 7 mm in diameter in a plate about
12 mm wide and 11 mm high.; outside a scrobicular ring, the plates covered with
small miliary tubercles of rather uniform size, or slightly decrease the sizes out-
159