the echinoid fauna from japan and adjacent regions part i

The Echinoid Fauna from Japan and Adjacent Regions 237
zadeki FOURTAU (1920, p. 22, pI. 2, figs. 6-7) and in jav. erbi (JEANNET and MARTIN,
1937, p. 236, text-figs. 12-15) (Fig. 20b) that the apical system is simple and dicyclic in
both genera. The genus Graphipleurus should be also identical with Brochopleurus, as
the former has a dicyclic apical system (ocular plates all exsert), a similarity of test
sculpture, and indistinct gill-slits also a similar feature. This is supported by the
fact that H. L. CLARK (loc. cit.) included a Javanese species, Arbacina cf. stellulata,
which is evidently identical with jav. rembangensis, the type-species of javanechinus,
in his genus.
This genus has a noteworthy resemblance to the Recent genus Desmechinus H. L.
CLARK, 1923 (H. L. CLARK, 1923-c, p. 342.-0rthotype-Des. anomalus H. L. CLARK,
1923-c, p. 342 (MCZ no. 4635).-MoRTENSEN, 1943, p. 341, pI. 20, figs. 31-32, text-figs.
199-200-China Sea), particularly with respect to the sculpture of the test. But the
simple and dicyclic apical system of this genus, together with the shallow gill-slits,
and single series of the pore-pairs, show it to be more primitive than Desmechinus.
In Desmechinus the apical system is more or less obliquely elongate towards the
genital (1), and the ocular (I) and (II) may be broadly insert, and gill-slits are sharp.
MORTENSEN (1943, p. 341) assumed that the two species of javanechinus from the
Miocene of Java may be the ancestors of the Recent Desmechinus-species, viz., jav.
erbi of Des. anomalus, and jav. rembangensis of Des. rufus or versicolor (or both).
There is a single species of this genus in our collection. It is described below.
Brochopleurus pulcherrimus NISIY AMA, n. sp.
(Pl. 5, figs. 12-15, pl. 6, figs. 4-5)
Holotype.-IGPS colI. cat. no. 73719.
Locality and geological horizon.-IGPS loco no. Ch-28.-In calcarerous sandstone
of sea-side cliff under the main road about 500:metres east of My6gane-zaki, Motona,
Hota-machi, Awa-gun, Chiba Prefecture. (tm Nago, Lat. 35°09'N., Long. 139°49'35/1E.).
Komayama formation, probably Lower Pliocene or Miocene. F. UEDA, 1931. Collected
by K. HATAI, K. KOTAKA, K. HATORI, and the writer.
There are four specimens of this species at the writer's disposal, the best preserved
one is selected as the holotype.
Dimensions of holotype.-9 mm in horizontal diameter, 5 mm in height.
Test small, thick, and rather low; ambital outline circular, aboral surface moderately
arched; adoral surface rather fiat, more or less concave near the peristome.
Apical system large, about 2.5 mm across; dicyclic, genital plates nearly an equal
size, pores distinct and placed near distal end, small tubercles on the plates seem
to be few in numbere; ocular plates nearly triangular in outline, and carry small
number of small tubercles, and all oculars exsert from the periproct. Periproct oval in
outline and 1 mm across in longer axis, all periproctal plates lacking.
Ambulacra rather narrow, about 3 mm wide at the ambitus; ambulacral plates
lower than the interambulacral plates, numbering 15-16 in one column, 1.5 mm wide
and 1 mm high at the ambitus, and composed of three components of the echinoid
structure, the pore-pair of middle demi-plate component produced slightly pushed
out of the general surface of two pore-pairs of aboral and adoral primary compo-