the echinoid fauna from japan and adjacent regions part i

The Echinoid Fauna from Japan and Adjacent Regions 17
angular suranal plates) and the Phymosomina MORTENSEN (without angular sur anal
plates), the latter comprising six families; among them the Hemicidaridae WRIGHT
and Pseudodiadematidae POMEL are removed from the Aulodonta, and placed in this
order based on the stirodont character of teeth found in the members of these two
families through the researches of MORTENSEN and others; the members of these two
families represent rather primitive stage in the development of this order. The small
and interesting family Tiarechinidae GREGORY were removed to this order from its
special and separate order Plesiocidaroida; because their ambulacral structure bears
a primitive character of primary plates throughout-in accordance with the fact that
it is also the oldest among the order. The assignment of these families to the order
seems to justify in their natural affinities.
By excluding the families, by MORTENSEN, of the Echinothuriids, the Hemicidarids,
the Pseudodiadematids, and the Orthopsids from the order Aulodonts, in which they
had been included by JACKSON and CLARK, the first family to the order of the Lepidocentroids,
the second and third to the order of the Stirodonts, and the fourth to the
Drder of the Camarodonts, the order of the Aulodonts have thus become clearly
restricted and approached more closely to the nature. MORTENSEN divided the order
into three suborders on account of the difference of structures of the primary spines.
After the discovery of the remarkable structure of the spines of the Aspidodiadematids,
so entirely different from the simple structure of the Diadematid spines, he maintains
that the Aspidodiadematids probably originated from some Palaeozoic Lepidocentroids,
and may represent a separate branch of or without direct connexion with, the
Diadematids: -the Aspidodiadematids form a separate suborder, the Aspidodiademina
MORTENSEN. The structure of the spines (the solid axis) of the Pedinids clearly
disprove the derivation of them from the Diadematids, the spines of which are charcterized
by their hollow axis: MORTENSEN agrees with BATHER'S and MERCIER'S
view that the Pedinids were derived from the primitive Cidarids, such as Triadocidaris.
Pedinids themselves form a special suborder, the Pedinina MORTENSEN. The hollow
spines of the Micropygids and the Diadematids are fundamentally different from those
of the Aspidodiadematids and the Pedinids. MORTENSEN also suggested that the
Micropygids-Diadematids must be derived from the Lepidocentroids. Accordingly
the Aulodonta are not a natural order as described above, but comprise three quite
different groups (suborders), each of the independent origin. This classifactory scheme
of this order is practical, and shows clear distinction of each group.
The discovery of the camarodont character of teeth (masticatory apparatus) in
Orthopsis by SERRA (1934, p. 51) and the general resemblance of the Glyphocyphids
to the Temnopleurids make the origin of the order of the Camarodonts not from
single source, but along two or three separate lineages. The perforate, non-crenulate
tubercles of Orthopsis, combined with the primitive character of the ambulacra, point
towards the more primitive forms of the Pedinids as the source from which it evolved;
this procedure, however, is open to later criticism. The family of the Glyphocyphids
stand apart from other families of the Camarodonts, excepting for the Orthopsids,
by their diadematoid ambulacra and their perforate, crenulate tubercles. The lantern
is not known of any Glyphocyphids, so that there is no proof whether the Glyphocyphids
really belong to either of the Camarodonts, the Stirodonts or to the Aulodonts.