ECHINODERMATA - KU ScholarWorks - University of Kansas

BLASTOID STUDIES 27
The description is taken mainly from one specimen
illustrated on Plate 3, figures 7-9.
Remarks.—The genus Cryptoschisma was probably
derived from Pentremitidea by outward migration of the
lancet plate to the surface of the calyx and fusion of the
subdeltoid and superdeltoid into an epideltoid.
Occurrence.—Devonian, Spain; Calizas de Arnao,
Saber°, and Calizas des Ferrofies, Le6n and Asturias.
Types.—Topotypes, 311, six specimens, DeKoninck
collection, old no. 2,357, Sabero, Spain, Harvard Museum
of Comparative Zoology, Cambridge, Mass.; 220, three
specimens, old no. 857, J. M. Barnard collection, labelled
Eifel, in Harvard Museum; and S3,224, 20 specimens,
Springer collection, Asturias, Spain, and S3,225, 16 specimens
Springer collection, León, Spain, in U.S. National
Museum, Washington; E1,063b, thin section, British Museum
Natural History.
Genus DECASCHISMA Fay, n. gen.
Type-species, by original designation (herein).—Codaster pentalobus
HALL, 1882 (adv. pub!., 1879).
Generic diagnosis.—Fissiculate blastoids with ten
exposed hydrospire fields, superdeltoid, subdeltoid,
hypodeltoid, lancet covered by side plates, exposed
spiracular slits, calyx conical in side view. Silurian,
Indiana.
DECASCHISMA PENTALOBUS (Hall)
Plate I, figures 7-10; text-figs. 18-20
Codaster pentalobris HALL, 1879, p. 13; 1882, p. 69.
Description.—Calyx calcitic, obconical in side view,
pentagonal in top view, 17 mm. long by 13 mm. wide,
with vault 5 mm. long, pelvis 12 mm. long, and pelvic
angle 50 degrees. Periphery well above mid-height at
radial lips. Stem impression worn, but in one specimen
it appears to be round, smooth, about 1 mm. in diameter,
with a small round central lumen. Basal circlet elongate
conical in side view, rounded pentagonal in basal view,
6.5 mm. long by 7.5 mm. wide, with three normally disposed
basals and small flat truncated aboral end. Radials
five, elongate hexagonal, each strongly lobed, giving the
calyx a broadly stellate appearance in top view, with short
limbs on anal side. Each radial is 11 mm. long by 5.5 mm.
wide, with broad, deep, short sinus 5 mm. long by 3 mm.
wide by 2 mm. high, projecting ventrally into low corona l
processes except on the anal side. Radials overlap deltoids.
Deltoids four, short, lancet-shaped, not visible in side
view, each 2 mm. long by 2.5 mm. wide, with wide V-
shaped deltoid lip, low medium septum, high deltoid
body, and seven or eight hydrospire slits on each side of
an ambulacrum with four or five exposed, the slits extending
across the adjacent radial limbs. On the anal
side there are three deltoid plates, a superdeltoid, subdeltoid,
and hypodeltoid. The superdeltoid is adjacent to
the oral opening, is broadly arrow-shaped, and adjacent
to lancet plates on each side. It is overlapped internally
by a thin long V-shaped subdeltoid, which is extended
on either side of the wide anal opening, beneath marginal
parts of the adjacent lancet plates. The subdeltoid limbs
are overlapped by the truncated radial limbs aborally, and
on the outside, the long wide pentagonal hypodeltoid
plate covers the subdeltoid limbs. The hypodeltoid can
be seen in side view, is low, abuts against the radial limbs,
and is approximately 4 mm. long by 4 mm. wide. Internally,
the subdeltoid limbs and adjacent radial limbs
are infolded into approximately three hydrospire slits on
either side of the anal opening. Thus there are three anal
deltoids and ten hydrospire fields, with a reduced number
of slits in the two fields on the anal side.
Ambulacra five, short, linear, each 7 mm. long by 1
mm. wide, with lancet covered by side plates and 36 side
plates in 10 mm. Side plates normally disposed, with a
subtriangular secondary side plate on the abmedial-adoral
corner of each subquadrangular primary side plate. The
surfaces of the calyx plates are ornamented with fine
growth striae parallel to the margins.
Remarks.—The genus Decaschisma appears to have
been derived from Polydeltoideus by fusion of the two
cryptodeltoids into a single subdeltoid plate.
Occurrence.—Silurian, Waldron Shale, Waldron,
Indiana.
Types.—Topotypes, 2,554, eight specimens, Washburn
collection, Walker Museum, University of Chicago, Chicago,
Ill. The description is based upon characters seen
in the specimen figured on plate 1, supplemented by features
of the other specimens.
DECASCHISMA PULCHELLUM (Miller & Dyer)
Plate 1, figures 1-3; text-figs. 21, 22
Codaster pulchedus MILLER & DYER, 1878, p. 35, pl. 2, figs. 13, 13a.
Description.—Calyx calcitic, obconical in side view
with flaring base, pentagonal in top view, 10 mm. long
by 7.5 mm. wide, with periphery well above mid-height
at radial lips, vault 2 mm., pelvis 8 mm., and pelvic angle
on basals 95 degrees, but on radial bodies 25 to 30 degrees.
Stem impression small, round, crenellar, 0.5 mm. in
diameter, on small flat triangular aboral portion of basals.
Basal circlet widely flaring, almost cup-shaped in side
view, 3.5 mm. long by 6 mm. wide, strongly triangular
in basal view, with a sharp ridge in the middle portion
of each basal plate extending to aboral end, forming a
sharp triangular base about 1 mm. in diameter. The
geometric center of each basal is flared outward, giving
a bluntly conical shape to the base in side view. Radials
Five, elongate hexagonal to subquadrangular, each 7 mm.
long by 4 mm. wide, with short, deep, wide sinus 2.5