ECHINODERMATA - KU ScholarWorks - University of Kansas

BLASTOID STUDIES 29
mm. long by 2 mm. wide by 1.5 mm. deep, forming part
of the summit; radial limbs overlapping deltoids.
Deltoids four, lanceolate, each 2 mm. long by 1 mm.
wide, not visible in side view, with a broad V-shaped lip,
deep septum, and high body projected into a low coronal
process, with approximately eight or nine hydrospire
slits on each side of an ambulacrum, of which four or five
are exposed. The slits extend to the adjacent radial limbs,
parallel to the lancet plate. On the anal side there are
three deltoid plates, superdeltoid, subdeltoid, and hypo-.
deltoid. The broad V-shaped superdeltoid is adjacent to
the oral opening, the elongate V-shaped subdeltoid resting
on the internal aboral surface of the superdeltoid.
The subdeltoid has two limbs that extend aborally on
either side of the anal opening and partly beneath the
adjacent lancet plates, folded internally into three hydrospire
slits on each side, the limbs being overlapped by
the adjacent radial limbs, and hydrospire slits extended
to the radial limbs. The large pentagonal hypodeltoid,
1.25 mm. long by 1.75 mm. wide, visible in side view,
covers parts of the subdeltoid limbs and abuts against the
radial limbs.
Ambulacra fi ve, short, linear, each 3 mm. long by 1
mm. wide, lancet being completely covered by side plates,
of which 35 occur in 10 mm. Primary side plates subquadrangular,
with subtriangular secondary side plates on
bevelled abmedial-adoral corner. The surfaces of the calyx
plates are ornamented with fi ne growth striae parallel to
the margins.
Remarks.—This species may readily be distinguished
from D. pentalobus by the flaring basal circlet, not present
in D. pentalobus.
Occurrence.—Silurian, Waldron Shale, Waldron, Indiana.
Types.—Topotypes, 2,810, 11 specimens, Washburn
collection, Walker Museum, University of Chicago, Chicago,
Ill. The description is based mainly on characters
seen in the specimen figured on plate 1.
Genus DELTOSCHISMA Fay, n. gen.
Type-species, by original designation (herein).—Phaenoschisma
archiaci ETHERIDGE & CARPENTER, 1882.
Generic diagnosis.—Fissiculate blastoids with ten
exposed hydrospire fields, four anal deltoids or a superdeltoid,
two cryptodeltoids, and a hypodeltoid, a reduced
number of slits on the anal side, lancet covered
by large side plates, calyx steeply conical in side view,
strongly pentalobate in top view. Devonian, Spain.
DELTOSCHISMA ARCHIACI
(Etheridge & Carpenter)
Plate 1, figures 4-6; text-figs. 23-25
Phaenoschisma archiaci ETHERIDGE & CARPENTER, 1882, pp. 229-
230.
Description.—Calyx calcitic, steeply conical in side view,
pentagonal in top view, 13.5 mm. long by 7 mm. wide,
periphery at radial lips, with vault 1 mm. long, pelvis 12.5
mm. long, and pelvic angle 30 degrees. Stem round, with
preserved part 4 mm. long by 2 mm. wide. Each columnal
is 0.75 mm. long, smooth, with smooth facets and small
round lumen. An enlarged columnal occurs at the aboral
extremity of the basal circlet, with a tripartite proximal
facet, each part concave upward to fit against the convex aboral
ends of the basal plates. Basal circlet steeply conical in
side view, rounded in basal view, 7.5 mm. long by 6 mm.
wide, enlarged at base, with the apex of a strongly triangular
ridge near the geometric center of the aboral
one-fourth of each basal. Radials five, each hexagonal, 7
mm. long by 3.5 mm. wide, with wide, short flaring sinus
2.5 mm. long by 2 mm. wide. In top view each radial
plate appears lobed near the radial lip and a slight constriction
is seen along each interradial suture, giving a
slight pentalobate appearance to the calyx in top view;
radials overlapping deltoids.
Deltoids four, lanceolate, not visible in side view, each
1.75 mm. long by 1.5 mm. wide, with approximately
eight hydrospire slits on each side of an ambulacrum,
parallel to the lancet plate, and continuing aborally to
the adjacent radial limbs. Approximately four hydrospire
slits are exposed along the steep sinus walls, the other four
being only partly exposed. The four hexagonal deltoid
lips are adjacent to the oral opening and connected to
the deltoid body by a low medium septum that is prominent,
thus giving the appearance of eight spiracular slits
around the oral opening. On the anal side there are four
deltoid plates, a hexagonal superdeltoid, two thin long
cryptodeltoids (mostly destroyed) on either side of the
anal opening, and a pentagonal hypodeltoid (missing, but
facets present) on the aboral side of the anal opening.
The hypodeltoid would abut against the truncated radial
limbs if preserved in place. The aboral ends of the
cryptodeltoids are destroyed, but ETHERIDGE & CARPENTER
(1886, p. 277) report that a reduced number of slits are
present on either side of the anal opening. Thus there
are ten hydrospire fi elds, the number of slits being reduced
on the two anal fields; four anal deltoids occur.
Ambulacra five, linear, short, each 3 mm. long by
1 mm. wide, the lancet being covered by side plates, with
a total of eight side plates in each ambulacrum and 30
side plates in a space of 10 mm. Each primary side plate
is subquadrangular with a secondary side plate on the
abmedial-adoral corner of each, with about four main
cover-plate sockets to each side plate along the main food
groove and four side cover-plate sockets along each side
food groove. The surfaces of calyx plates are ornamented
with fine growth striae parallel to the margins.
Remarks.—The genus Deltoschisma is the most primitive
European blastoid known to date. It is similar to
Polydeltoideus of the Silurian of North America but