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96 THE UNIVERSITY OF KANSAS PALEONTOLOGICAL CONTRIBUTIONS
PLACOBLASTUS ERIENSIS (Reimann)
Plate 32, figures 1-3; text-fig. 202
Nucleocrinus verneuili eriensis REIMANN, 1935, p. 33, pl. 4, figs. 4-5.
Description.—Calyx ellipsoidal in side view, broadly
rounded pentagonal in top view, 26 mm. long by 18 mm.
wide, with periphery near mid-height, and flat summit,
with flat base. Basal circlet pentagonal in aboral view,
2 mm. wide, with small round stem 0.5 mm. wide in
sharp central basal concavity. Each basal plate has a high
round ridge extending radially from the center of each
plate toward the radial lips, except on the "D' ambulacral
side. The ridge on the azygous basal bifurcates into
two low rounded ridges that extend to the "A" and "B"
radial lips. Radials five, each 6 mm. long by 5 mm. wide,
elongate pentagonal in side view, with a broad M-shaped
radiodeltoid suture. Radial sinus short, 2 mm. long by
1 mm. wide. Deltoids overlap radials.
Deltoids four, each broadly lenticular, 23 mm. long
by 9.5 mm. wide, with smooth central triangular area
flanked on either side by lenticular nodose areas, similar
to that of Nucleocrinus. The adorai tips of each deltoid
are notched by two elongate hemielliptical spiracles, one
on each side adjacent to the ambulacra. On the anal side
there are at least three anal deltoids, the two elongate
lenticular cryptodeltoids, with the elongate quadrangular
hypodeltoid between. On the adoral side of the anal
opening one large plate occurs between the adorai ends
of the cryptodeltoids, and possibly there is another plate
below it. The upper plate is here interpreted to be an
accessory anal oral, but it could be superdeltoid and the
plate below could be part of the upper one, with a crack
between, instead of a suture. There are five large oral
plates covering the summit, each broadly triangular and
interambulacral in position and (depending on interpretation)
one accessory oral is recognized between the adorai
tips of the cryptodeltoids. One hemielliptical spiracle is
present in the adorai tip of each cryptodeltoid along the
ambulacral margins. Thus, 11 openings surround the
oral aperture, consisting of ten spiracles and a separate
anal opening. Ornamentation of deltoids and anal deltoids
is similar to that of Nucleocrinus.
Ambulacra five, linear, each 29 mm. long by 1 -mm.
wide, recurved below, with lancet covered by side plates,
and 28 side plates in a space of 10 mm. along an ambula-
FIGURE 202. Placoblastus eriensis (REimANN), Ludlowville
Formation, Springbrook, New York (Buffalo Soc.
Nat. Sci., no. E11,811); summit and anal areas, X10.6.
[Explanation.—An, anal opening; CR, cryptodeltoid; D,
deltoid; HD, hypodeltoid; 0, oral plate; S, spiracle; Su,
superdeltoid.]
crum. Side plates and pores disposed as in Nucleocrinus,
with inner side plate present.
Remarks.—This and other species of Placoblastus may
be distinguished by shape, relative proportions of plates,
and disposition of orals.
EXPLANATION OF PLATE 31
FIGURE PAGE
1-9. Placoblastus obovatus (BARRis), ?topotypes, E21,115 (figs.
1-7,9), E21,113 (fig. 8), Buffalo Soc. Nat. Sci.; Middle
Devonian, Thunder Bay Limestone, Partridge Point, near
Alpena, Mich. 1 3. Oral, aboral, and "D" ambulacral
views of uncrushed specimen ( X 1.5).-4-6. Oral, "EA"
interambulacral, and aboral views of slightly crushed
specimen with oral plates in place ( X 1.8).—Aboral end
of "C" ambulacrum of specimen illustrated in fig. 5,
showing main, outer, and inner side plates on polished
surface (X31.5).-8. Cross section (polished) of another
specimen showing deep bifurcation of two hydrospire
folds on each side of an ambulacrum ( X 11.5).-9. Oral
view of specimen shown in fig. 4, showing five large oral
plates and large additional plate between adorai tips of
cryptodeltoids ( X 5.4) 94