the echinoid fauna from japan and adjacent regions part i

156 S. NISIYAMA
Primary spines rather stout, moderately long, and a little narrowed near the baser
where they are nearly circular in section. Farther up the shaft they are compressed
laterally, elliptical in section, the lateral margins being sharp and regularly serrated,.
the small scale-like projections inclined outward, and toward the apex of shaft. On
the both surfaces of flattened shaft are six longitudinal series of similar serrations·
more or less smaller than those of the laterals. Number of serrations is counted
eight to ten in the space of one millimeter. Collar low with milled ring; base concave,
not oblique.
The primary spines of this species are very characteristic and there are no
comparable spines among the genus Miocidaris. There arises a question that the
spines of the preceding species (M. spinulifera) and those of this (M. platyacantha)
may be belong to one and the same species, as the spines of the former represent
the aboral or ambital ones and those of the latter the oral spines of a species, as·
seen in the case of the Recent species of the genus Histocidaris, especially in H.
magnifica MORTENSEN (MORTENSEN, 1927, p. 245, pIs. 48-49, pI. 76, figs. 1-3, text-figs.
1-3). In H. magnifica, the aboral spines long, taper to point, perfectly smooth,
shining, without any serrations, but the oral primaries are curved, flattened, strongly
serrate, and ending abruptly as if worn off. The primaries of M. platyacantha,
however, are not curved and the primaries of M. spinulifera have spinules being not
smooth as in H. magnifica, and the two types of the primaries did not occur together,
but found separately. There is no positive proof that they belong to one and the
same species, so the writer here treated them as two distinct species.
Family CIDARIDAE GRAY, 1825
Cidaridae GRAY, 1825, p. 426.-Cidaridae MULLER: A. AGASSIZ, 1872-74, p. 96.-DuNCAN,
1889-a, p. 25 (pro parte).-GREGORY, 1900-b, p. 302.-H. L. CLARK, 1907, p. 172.-JACKSON,
1912, p. 202.-H. L. CLARK, 1925, p. 1.-Cidaridae GRAY: MORTENSEN, 1928-b, p. 61.­
Cidaridae MULLER: GRANT and HERTLEIN, 1938, p. 4.-Cidaridae GRAY: DURHAM and
MELVILLE, 1957, pp. 251, 252.
Type-genus.-Cidaris LESKE, 1778
Stereocidarinae LAMBERT, 1900, p. 49.-LAMBERT and THIERY, 1910, p. 129.-MoRTENSEN,-
1928-b, p. 68.
Type-genus.-Stereocidaris POMEL, 1883
Interambulacra with only two columns of usually solid plates, in one case,
Tetracidaris COTTEAU (1873-a, p. 163) there are four columns of interambulacrals,
but only at the ambitus, not in the adoral part of test; rigid sutures. Primary
spines very diverse, though in the main cylindrical or club-shaped, sometimes (Goniocidaris
AGASSIZ and DESOR, 1846, p.337) the upper ones shield-shaped. Pores nonconjugate
or conjugate, arranged in simple series. Primary tubercles crenulate or
non-crenulate. Pedicellariae typically in three forms, large and small globiferous·
and tridentate, but sometimes one or the other of these forms may be lacking.
Moderate, to large forms, more rarely small, ranging from the Jurassic Period
to the Recent seas.
DURHAM and MELVILLE (1957, p. 252) restricted the family Cidaridae to those
having 20 columns of plates (with the exception of Tetracidaris) in a rigid corona
and are equivalent to "Stereocidarinae" as used by MORTENSEN (1928-b).