ECHINODERMATA - KU ScholarWorks - University of Kansas

BLASTOID STUDIES 23
lapping deltoids, with broad sinuses. Lower Carboniferous,
England.
CODASTER ACUTUS M'Coy, 1849
Plate 12, figures 1-7, 9; text-figs. 8, 9
Codaster acutris M'Coir, 1849, pp. 250-251.
Description.—Calyx calcitic, cup-shaped in side view,
pentagonal in oral view, 14 mm. long by 11 mm. wide,
slightly compressed, with flat summit and rounded base.
Stem round, crenellar, with small round lumen. Basal
circlet cup-shaped in side view, rounded pentagonal in
basal view, large, 6.5 mm. long by 9 mm. wide, with a
prominent bluntly rounded median ridge on each basal
plate. Radials five, pentagonal in side view, wide, each
9 mm. long by 8 mm. wide, with flat truncated top bearing
sinuses so that the ambulacra are almost invisible in
side view. Each radial sinus is 2 mm. long by 5.5 mm.
wide, with deltoids overlapped by thickened radial limbs.
Deltoids four, short, lancet-shaped, each 6 mm. long
by 3 mm. wide, confined to summit, with low crests, and
with approximately eight hydrospire slits exposed on each
side of an ambulacrum except in anal area where they
are lacking. The slits extend to the adjacent radial limbs.
Approximately 16 cover plate sockets occur on each side
of each deltoid lip. On the anal side, the thick horseshoeshaped
epideltoid, adjacent to the oral opening, surrounds
the adorai portion of the anal opening on three sides and
is overlapped by the radial limbs. The aboral part of the
anal opening was presumably covered by a pentagonal
hypodeltoid which is missing, probably as a result of
disturbance of sediment in which it was buried, judging
from the worn nature of the theca. Hydrospire slits are
lacking on anal side and therefore only eight hydrospire
fields are developed.
Ambulacra five, short, petaloid, confined to summit,
each 3.75 mm. long by 1.75 mm. wide, with the adorai
end of lancet 2 mm. from oral opening and exposed between
side plates for a short distance aborally, but generally
covered by side plates. Primary side plates subquadrangular,
30 in a length of 10 mm., with a subtriangular
secondary side plate on the adoral-abmedial corner
of each primary side plate. The brachiolar area of
attachment is shared equally between a primary side
plate and its associated secondary side plate. Approximately
four main cover-plate sockets correspond to each
side plate along the main food groove and three side
cover-plate sockets along either side of each side food
groove. Surfaces of calyx plates are ornamented with
fine growth striae parallel to plate margins.
Remarks.—The genus Codaster is a specialized form
that, as now understood, should be restricted to fossils
known from the Lower Carboniferous of England. It was
probably derived from a form like Trionoblastus of the
Devonian, in which the superdeltoid and subdeltoid plates
are fused to form the epidcltoid.
Occurrence.—The labels on the specimens are generalized
and merely indicate unspecified Lower Carboniferous
strata of Yorkshire, Lancashire, and Derbyshire,
England.
Types.—Plesiotypes 367, six specimens, Harvard Museum
of Comparative Zoology, Cambridge, Mass. The
description was based mainly on characters of one of
these specimens, with an old name "Pentremite asteria"
and number 2319, Malham, Yorkshire, England, on the
label. Plesiotypes 96,267, three specimens, Carboniferous
limestone, Yorkshire, England, labelled Codaster acutus;
S3,200, three specimens, Carboniferous limestone, Lischowney,
Derbyshire, England, labelled Codaster acutus,
Springer collection; S3,218, two specimens, Carboniferous
limestone, Lancashire, England, labelled Codaster
trilobatus, Springer collection; S3,219, three specimens
of the Hambach collection, Carboniferous limestone,
Lischowney, Derbyshire, England, labelled Codaster trilobatus
in the Springer collection; and S3,220, two specimens,
Carboniferous limestone, Settle, Yorkshire, England,
labelled Codaster trilobatus var. acutus, Springer
collection, U. S. National Museum, Washington.
Genus CONOSCHISMA Fay, n. gen.
FIGURES 8, 9. Codaster acutus M'CoY, Lower Carboniferous,
England; part of "A" ambulacrum showing main
and outer side plates seen in two specimens (Harvard
Mus. Comp. Zoology, no. 367, fig. 8, X45; U. S. Natl.
Mus., no. S3,218, fig. 9, X37.5). [Explanation.—Bf,
brachiolar facet; Bp, firachiolar pit; OSp, outer side plate;
Sp, main side plate.]
Type-species, by original designation (herein).—Codarter (Cryptoschisma?)
iaeviusculus ROWLEY, 1900.
Generic diagnosis.—Fissiculate blastoids with ten
exposed hydrospire fields, an epideltoid and hypodeltoid,
broad radial sinuses, lancet covered by side plates,
ambulacra extending down sides of theca; form of
calyx conical in side view. Mississippian, Missouri.