the echinoid fauna from japan and adjacent regions part i

216
Horizontal diameter
Height
Apical system
Peristome
Number of ambulacral plates
Number of interambulacra plates
Thickness
S. NISIYAMA
No. 27439
45mm
24
"
8
"
11
29
20
2.5mm
No. 22242 No. 58345
37mm 33mm
20
7
"
17
6
"
10
27
"
9
26
18 17
2mm
Test large, thick and stout, low (less than two-thirds of horizontal diameter of
test), and fiat; apical system is lost from all the specimens, vacant area small (less
than one-fourth of horizontal diameter of test); angular pits of ambulacral and
interambulacral areas large, sharp and bevelled, united into one at the median
suture on aboral surface (see figs.!, 2 of the fossil specimen, and figs. 3, 4 on plate
4 of the living specimen), usually elongate triangular in outline and pointed inward.
In the largest specimen, ambulacra narrow, about 10 mm wide at the ambital
region; poriferous zones slightly sunken and narrow, about 1 mm wide at the
ambitus, pore-pairs in triplets and in a nearly vertical series close to margin of
the area, pore-pairs of middle demi-plate component slightly produced outward
from the level of the two pore-pairs of aboral and adoral primary components;
primary tubercles on ambulacra as large as those on interambulacra, the large primay
tubercles very prominent and decidedly larger than the small primary (or large
secondary) tubercles (which as large as the moderate secondary tubercles); large
primary tubercles form a prominent vertical series on each side of interporiferous
area near the poriferous zone; small primary tubercles form also a vertical series inside
the large primary series; moderate secondary tubercles placed inside rather regularly
on the plates and above the large primary tubercle; small secondary and miliary
tvbercles cover the rest of plates, forming close circles around the large and small
primary tubercles; along median line there is a depression united to angular pits.
Interambulacra broad, about 16 mm wide at the ambital region; interambulacral
plates rather low, 8 mm wide and 3 mm high; large primary tubercles very prominent
and decidedly larger than the small primary tubercles, being placed somewhat eccentrically
and adorally, and form a prominent vertical series; small primary tubercles
form two vertical series at the ambital region, one inside and the other outside of
the large primary series, almost as large as the moderate secondary tubercles; moderate
secondary tubercles placed rather in horizontal row above the large tubercles;
small secondary and miliary tubercles cover the rest of plates, forming circles around
the large and small primary (or large secondary) tubercles. Primary tubercles distinctly
crenulate, number of crenulation on the large primary tubercles seems to be
constantly 12.
From the specific character of these specimens, they may safely be identified
with the Recent Tem. hardwickii (GRAY, 1855), which ranges from northern japan to
western japan, around off Kobe, in geographical distribution, and commonly found
in littoral waters (5 to down 35 metres) of northeastern japan. This species is a
unique boreal form of the genus, and seems to have descended from the related
species of older occurrence, i. e., Tem. toreumaticus, by the specialization of the