the echinoid fauna from japan and adjacent regions part i

The Echinoid Fauna from Japan and Adjacent Regions
ed in various and uncertain forms; but by removing of the families of the Hemicidarids
and' Pseudodiadematids from this order by MORTENSEN (1935, pp. 384, 417)
and, DURHAM: and' MELVILLE. (1957, pp. 253, 254) to the order of the Arbacioids, the
order of the Diadematoids becomes much more natural in the classification and: affinities
of the Echinoidea.
MORTENSEN believed (1935, p. 5) that the, families of the order Diadematoida
(with the exclusion of the Echinothuriids) appear to represent three different stems,
mainly founded on the, structural characters of their spines, and on their probable
sources. and, that these three parallel, but separate stems, each originating from its.
own source. On recognizing the three separate stems, MORTENSEN claimed the, necessity
to separate them into three suborders; i. e., the Aspidodiademina, Diademina, and:
Pedinina; he believed that his suborders Diademina and Pedinina, are of independent
origin, the former having been derived from the Palaeozoic Echinocystitids, and the,
latter from the Cidarids. DURHAM and MELVILLE (1957, p. 253) disregarding, MORTEN­
SEN'S derivation of the Diademina from the Echinocystitids, believe a Cidaroid ancestry
for Diademina and Pedinina; they proposed the e-levation of each to ordinal rank.
They associated also the Aspidodiadematidae with the Diadematidae and Micropygidae
in their order Diadematoida.
The Echinothuriids; the much discussed and disputed forms, which are regarded
by MORTENSEN (1934, 1935) as the survivors of the Palaeozoic Echinocystitids, may
be associated; as claimed by DURHAM and MELVILLE (1957, pp. 250-251), with the·
Pedinids. DURHAM and MELVILLE (1957, pp. 246-247, 253) have separated the Pygasterids,
which, are formerly classified with the Holectypids, from the true Holectypoids,
and erected a new Order Pygasteroida (p. 253), for the Pygasterids have a
close affinity the Diadematoids, and would be ascribed to a Pedinoid ancestry; this.
belief had already been stated by MORTENSEN (1948-b, p. 10).
Only a fossil representative of the suborder Diadematoina is in our collection.
Suborder DIADEMA TOlNA DUNCAN, 1889
Diadematoida DUKCAN, 1889-a, p. 24 (pro parte).-Diademina GREGORY, 1900-b, p, 308.­
MORTEKSEN, 1904, p. 55 (tribus).-MoRTENSEN, 1939, p. 547.-MoRTENSEN, 1940, p. 136,­
Diadematina GREGORY: NISIYAIVIA, 1954, p. 325 (in Japanese).-Diadematoida Dc:\cA:\:
DURHAlvl and MELVILLE, 1957, p. 253 (order).
Type-family.-Diadematidae GRAY, 1855
Regular Echinoids with aulodont teeth and ambulacra consisting of generally
compound, plates of the diadematoid structure; coronal plates generally imbricating
or rarely rigid; radioles (spines) hollow, only exceptionally the axis is filled by a
loose meshwork. Primary tubercles perforate and crenulate or rarely non-crenulate.
From the Lower Jurassic (Lias) to Recent.
This suborder comprises three families, and they are distinguished from each
other by the following key (after MORTENSEN, 1940).
Key to the families of the suborder Diadematoina.
1. Primary spines with the axis divided into compartment, separated by fenestrated
transverse plates (dissepiments), connected by long, thin threads. Tubercles
strongly crenulate. Ambulacra consisting of simple or compound plates of