the echinoid fauna from japan and adjacent regions part i

176 S. NISIYAMA
diadematoid structure. Apical system large, monocyclic, oculars large and all
insert. Periproct leathery, only partially plated........ Aspidodiadematidae
Primary spines (usually) with hollow axis; tubercles crenulate or non-crenulate .. 2
2. Tubercles non-crenulate_ Tube-feet of the outer series transformed into large,
umbrella-shaped organs, contammg anchor-shaped . spicules. Pore-pairs
arranged in double series .................................... Micropygidae
Tubercles (usually) crenulate. Tube-feet of the outer series not transformed into
large, umbrella-shaped organs. No anchor-shaped spicules. Pore-pairs not
arranged in double series .................................... Diadematidae.
The distinction of the diadematids from the Micropygids by the character of
-tube- feet, as described above, does not apply to the fossil forms, as the tube-feet
are not preserved in a fossil state, but the distinction by the character of tubercles
(crenulate and non-crenulate) and arrangement of pore-pairs safely guarantee the
families of the fossil forms.
The family Micropygidae MORTENSEN (MORTENSEN, 1904, p. 45.-DoDERLEIN, 1906,
pp. 86, 169.-MoRTENSEN, 1940, p. 136) related to the Diadematidae in the structural
-character of the spines. The family of the Micropygids may be regarded as a sidebranch
from the Diadematids, or perhaps it has arose directly from the Cidarids as
a small separate, specialized stem parallel with the Diadematids. There is nothing
of our knowing, however, of any fossil forms linking the Micropygids with the
Cidarids. The small family Aspidodiadematidae DUNCAN, 1889 (DUNCAN, 1889-a, p.
56.-A. AGASSIZ and H. L. CLARK, 1908, p. 59.-MoRTENSEN, 1940, p. 6), which differ
more or less in the structural character of spines from that of the Diadematids, may
represent a separate branch, originating separately from some unknown form of the
'Cidaroids.
Only a fossil of a genus of the Diadematidae is represented in our collection.
Family DIADEMATIDAE GRAY, 1855
Diademadae GRAY, 1855, p. 35.-Diadematidae PETERS, 1855, p. 106.-Diadematidae GRAY:
WRIGHT, 1857-78(57), pp. 18, 106.-Diadematidae PETERS: COTTEAU, 1861-67(61), p.
78.-DESOR and DE LORIOL, 1867-72(69), p. 88.-DE LORIOL, 1873, p. 67.-A. AGASSIZ,
1872-74, p. 407.-ZITTEL, 1879, p. 500.-COTTEAU, 1880-85(80), p. l.-Les Diadematiens
POMEL, 1883, p. 106.-Diadematidae PETERS: DUNCAN, 1889-a, pp. 57, 58.-GREGORY,
1900-b, p. 309.-DELAGE and HEROUARD, 1903, p. 230.-MEISSNER, 1904, p. 1356.­
MORTENSEN, 1904, p. 40.-A. AGASSIZ and H. L. CLARK, 1908, p. 103.-LAMBERT and
THIERY, 1910, p. 162.-H. L. CLARK, 1925, p. 40.-MoRTENSEN, 1940, p. 158.-TERMIER and
TERMIER, 1953, p. 894.
Centrechinidae JACKSON, 1912, p. 202.-GRANT and HERTLEIN, 1938, p. ll.-H. L. CLARK,
1946, p. 296.
Type-genus.-Diadema (HUMPHREYS, 1797) GRAY, 1825
Test of moderate to large size, usually more or less flattened; plates may be
rather strongly imbricating, the test then being more or less flexible. Ambulacra
consisting of simple or trigeminate compound plates of the diadematoid structure.
Apical system generally monocyclic, or the oculars partly insert; periproct more or
less plated, to nearly leathery, sometimes with anal tube. Peristome of moderate to
large size; gill-slits distinct. Primary ambulacral and interambulacral tubercles
perforate and crenulate, exceptionally non-crenulate. Spines typically hollow, mostly