the echinoid fauna from japan and adjacent regions part i

-30 S. NISIYAMA
ordinal ranks in the Echinoidea may be less than twenty, or even less. The writer
feels that the minor differences in the primitive Echinoids can not be so small as
hitherto thought, but considering their long geological range (e. g., the family of the
Echinocystitids range from the Lower Silurian to the Permian, almost three times as
long as the range of the family of the Glyphocyphids, and also ten times as long as
that of the family of the Echinometridsof the specialized forms), and comparing the
minor differences to those of the short-lived and specialized forms, morphologi.cal
change in the primitive forms should be of a slow rate, because it can be assumed
that the differences in the primitive forms must have a significance in the morphogenetic
development and in the classification of the class. But, unfortunately, as new
material of very rare forms of the primitive Echinoids has not been accessible to the
writer, the solution of this problem appears to be easily inaccessible to the writer
himself.
A key to the orders and suborders of the class Echinoidea, in the writer's mind,
js as follows (emended from MORTENSEN'S, DURHAM and MELVILLE'S, and others).
1. Regular Echinoids with interambulacra of 1-14 columns; ambulacra of 2-20
column's, without compound plates; periproct within apical system; perignathic
girdle only of apophyses, or none; teeth grooved; no branchial slits, no
sphaerida, no ophicephalous pedicellariae . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 2
Echinoids with interambulacra and ambulacra of two columns each; corona
generally rigid, rarely imbricating; periproct within or outside the apical
system; peri gnathic girdle of auricles, with or without apophyses, or absent
in adult; lantern with grooved or keeled teeth, or absent in adult; branchial
slits present, or absent in adult; sphaeridia present; ophicephalous pedicellariae
generally present .................................................. 4
2. Interambulacra of one or more than two, ambulacra of two or more; corona rigid,
but ambulacra level over interambulacra along adradial suture; base of corona
resorbed; genital plates present; tubercles imperforate; tubercles and spines
all small, of uniform size; peristome with ambulacral and some interradial
plates; lantern inclined; no perignathic girdle .. . . . . . . . . . . . . .. Palaechinoida_
(Melonechinoida)
Twenty or more columns of plates; if more than 20, the coronal plates are always
imbricate, or not; tubercles and spines usually of various sizes, primaries
and secondaries; ambulacra continuing over the peristome, there being series
of plates between mouth and edge of peristome .......................... 3
3. Corona imbricating, ambulacral plates imbricating adorally, interambulacral plates
adapicaUy and over the ambulacrals along the adradial suture; primordial
ambulacral and interambulacral plates in basicoronal row; genital plates present;
no perignathic girdle; primary radioles slender, without cortex layer;
lantern inclined ............................................ Echinocystitoida
(Lepidocentroida)
Interambulacra of two or four columns, and ambulacra of two; ambulacra narrow;
corona rigid, or imbricating as in the Echinocystitoids; base of corona resorbed;
genital plates present; one large primary tubercle on each interambulacral
plate; peristome with both ambulacral and interradial series of