ECHINODERMATA - KU ScholarWorks - University of Kansas

94 THE UNIVERSITY OF KANSAS PALEONTOLOGICAL CONTRIBUTIONS
five large arrow-shaped oral plates, each interambulacral
in position, the superdeltoid and adjacent adoral tips of
the cryptodeltoids abutting against the large anal oral.
The adorai tips of each deltoid are excavated by two semielliptical
spiracles along ambulacral margins, and each
adorai tip of each cryptodeltoid has one marginal slitlike
spiracle, separate from the anal opening. Thus, 11 openings
surround the oral aperture, consisting of ten spiracles
and a separate anal opening. The calyx plates are ornamented
as in Nucleocrinus. Two elongate hydrospires
occur on each side of an ambulacrum, with an elongate
hydrospire canal extending to each.
Ambulacra five, linear, recurved below, each 55 mm.
long by 2 mm. wide, with 23 side plates in a space of 10
mm. along an ambulacrum, lancet covered by side plates,
inner side plate large, and side plates disposed as in
Nucleocrinus. There is an inward-projecting hornlike
process on the inner medial wall of the hypodeltoid. Six
cover-plate sockets to each side plate are observed along
the main food groove.
Occurrence.—Middle Devonian, Thunder Bay Limestone
(or Partridge Point Formation), Partridge Point,
near Alpena, Michigan.
Types.— Topotypes?, E21,113, four specimens;
E21,115, two specimens, Buffalo Society of Natural Sciences,
Buffalo, New York. The description is taken from
the characters mainly seen in specimens E21,115.
PLACOBLASTUS ANGULARIS (Lyon)
Plate 32, figure 8; plate 33, figures 1-9; plate 34, figures 1-9; textfigs.
197-199
Olivanites angularis LYON, 1857, p. 492, pl. 5, figs. 2, 2a, 2b.
Nucleocrinus angularis LYON & CASSEDAY, 1859, p. 295.
Nucleocrinus powelli REIMANN, 1935, p. 34, pl. 3, figs. 4-6.
Description.—After careful comparison of the types
of P. powelli with P. angularis I have been unable to find
significant differences. The description is of a paratype
(E9,058) of P. powelli.
Calyx calcitic, 19 mm. long by 15.5 mm. wide, with
flat summit, slightly concave base, periphery slightly adoral
of mid-height, and interambulacral areas concave in
oral view. Basal circlet pentagonal in aboral view, 3 mm.
wide, flat to slightly concave, with round stem impression
1.5 mm. wide, with small round central lumen, and
three normally disposed basais. Radials five, each 5 mm.
long by 5.5 mm. wide, recurved below in basal concavity,
with sinus 1.5 mm. long by 1 mm. wide. The radiodeltoid
suture is broadly M-shaped. Deltoids overlap radials.
Deltoids four, bluntly lenticular, each 18 mm. long
by 8.5 mm. wide, each with a smooth central triangular
area with base almost full width of radiodeltoid suture,
bordered laterally by two lenticular areas of nodose ornamentation,
similar to those of Nucleocrinus. Each row of
nodes is aligned with a side plate, forming a high angle
with the median food groove. The aboral tips of the
nodose side regions extend aborally between each ambulacrum
and radial limb, forming a short wedge. On the
anal side there are at least three deltoids, the two elongate
lenticular cryptodeltoids with the elongate subquadrangular
hypodeltoid between, and probably a fourth (superdeltoid)
between the adorai tips of the cryptodeltoids. The
superdeltoid is covered almost completely by an anal oral
plate in approximately the same position, but in some
specimens there appear to be two plates fully exposed
in this region. Thus, six or seven oral plates cover the
summit, depending on interpretation of the plate that is
adjacent to the adoral side of the anal opening. There are
five large oral plates over the summit, each arrow-shaped
and interambulacral in position, with one or two accessory
oral plates on the anal side. At present, the interpretation
here presented is that two plates occur between the
FIGURE 197. Placoblastus angularis (LYON), Middle
Devonian, Ludlowville Formation, Springbrook, New
York (Buffalo Soc. Nat. Sci., no. E9,058); summit and
anal areas, X11.7. [Explanation.—An, anal opening; CR,
cryptodeltoid; HD, hypodeltoid; 0, oral plate; S, spiracle;
Su, superdeltoid.1