the echinoid fauna from japan and adjacent regions part i

The Echinoid Fauna from Japan and Adjacent Regions 33
sometimes opposite; genital pores four; no fasciole ............ Cassiduloida
Lantern present in the juveniles, but resorbed completely before the adult stage
is reached; ambulacra petaloid adapically ...................... Cassiduloina
Lantern present even in adult stages; ambulacra petaloid adapically; auricles
interradial in position ........................................ Conoclypoina
Lantern absent in adult stages; petals lacking, and adapical ambulacral plates with
single pores ................................................ Neolampadoina
17. Ambulacra more or less petaloid adapically or quite rudimentary; apical system
never to opposite peristome or sometimes opposite; no branchial slits; no
bourrelets; fascioles often present.................... . . . . . . . . .. Spatangoida
Plastron of primary, simple, primitive structure, very small not differentiated
labrum meeting at its posterior end joining two not specialized sternal plates;
apical system elongate or disjunct; no distinct fasciole .......... Collyritoina
Plastron meridosternous (labrum joining at its posterior end only a single plate
no. 2); fasciole of irregular occurrence; apical system generally elongate or
disjunct; petals, when present, not impressed .................. Urechinoina
Plastron amphisternous (labrum joining at its posterior end two large sternal
plates, equally, or nearly equally, developed); apical system compact, never
opposite to peristome; petals usually impressed, not all similar; fascioles
usually present ................................................ Spatangoina
It seems to the writer that no clear-cut division into two subclasses (the Regularia
(Endocycloida)-the periproct within the apical system and the Irregularia (Endocycloidea)-the
periproct outside the apical system in the posterior interambulacrum
(5)), in the class Echinoidea, is possible. The distinction between the two subclasses
is somewhat arbitrary and practical, because in some Regularia (i. e., Acrosalenia
AGASSIZ and Pygaster AGASSIZ) the periproct is just barely within or outside the
ring, and in some primitive Irregularia (i. e., Galeropygus COTTEAU) it lies scarcely
outside. From such a difference in the features to erect the higher rank like subclass
superior to order appears peculiar and is inacceptable to the writer. It also follows
that the division of the so-called Irregularia into two superorders, viz, Gnathostomata
(roughly corresponding to the Holectypoida and Clypeasteroida) and Atelostomata
(Cassiduloida and Spatangoida) is unnecessary.
TYPES IN THE GENUS-GROUP
The kinds and their names of type-species (ICZN, 1961, p. 63), which the writer
intends to use here, are followed, chiefly what have been used by the writer himself
(1937, pp. 47-60) and IREDALE (1939, pp. 209-425) : they are-
Orthotype: (ICZN, 1961, Article 68 (a))-(Type by original designation).
Example: Genus Hemicentrotus MORTENSEN, 1942
Hemicentrotus MORTENSEN, 1942, p. 23l.
Orthotype.-Psammechinus pulcherrimus A. AGASSIZ, 1863-a, p. 357
(Hakodate Bay, Japan).
Haplotype: (ICZN, 1961, Article 68 (c))-(Type by monotypy at the time).
Example: Genus Scaphechinus A. AGASSIZ, 1863