ECHINODERMATA - KU ScholarWorks - University of Kansas

64 THE UNIVERSITY OF KANSAS PALEONTOLOGICAL CONTRIBUTIONS
by side plates at aboral end and gradually exposed to
one-third of its width near the adorai end, with one
pore between side plates along deltoid and radial margins;
radials overlapping deltoids; calyx subglobular.
Mississippian, Illinois, Missouri, Kentucky, Alabama.
Remarks.—The genus Diploblastus was probably
derived from a form similar to Schizotremites in
which the lancet plates extended downward and the
form became subglobular. There should be more intermediate
forms.
DIPLOBLASTUS GLABER (Meek & Worthen)
Plate 48, figures 1-12; plate 49, figures 1-9; text-figs. 113-119
Granatocnnus glaber MEEK & WORTHEN, 1869, p. 91.
Granatocrinus glaber MEEK & WORTHEN, 1873, p. 537, pl. 20, fig.
I l.
Description.—Observations here recorded are based
mainly on one of the original syntypes. Calyx calcitic,
worn, flattened spheroidal in side view, rounded pentagonal
in top view, 5 mm. long by 6 mm. wide, with
periphery at mid-height. The stem is round, crenellar,
attached to a raised hexagonal base in the middle of the
basal circlet, with small round central lumen. Basal circlet
pentagonal in basal view, flat, 2.75 mm. in diameter, with
three normally disposed basals. In one specimen from
Kentucky the azygous basal is in the "DE" instead of
"AB" position, but this specimen may belong to another
species. Radials five, pentagonal in side view, recurved
below, each 4.5 mm. long by 3.25 mm. wide, with long,
narrow, shallow sinus 4.5 mm. long by 1 mm. wide.
Radials overlap deltoids.
Deltoids four, short, each 2 mm. long by 2 mm. wide,
broadly lanceolate, each with a paired spiracle at the
adorai tip. Four deltoid plates are present on the anal
side—a superdeltoid, two cryptodeltoids, and a hypodeltoid.
The V-shaped superdeltoid is adjacent to the
oral opening and has two deltoid septa that are continuous
in position with the cryptodeltoids. The adorai
end of the paired anispiracle is excavated in the superdeltoid.
Immediately aboral to the two septa and aligned
with them are two subquadrangular cryptodeltoids, located
on either side of the anal opening. The broad
pentagonal hypodeltoid rests on the cryptodeltoids and
covers the aboral part of the anal opening. The anal
opening is partly fused with the adjacent hydrospire
canals, thus forming a paired anispiracle on the anal
side. Therefore, five spiracles surround the oral opening
—four paired spiracles and a paired anispiracle. In
weathered specimens these openings are separate and a
variable number appear to be present from specimen to
specimen. There are two hydrospire folds on each side of
an ambulacrum, without a hydrospire plate.
Ambulacra five, linear, recurved below, each 7.5 min.
long by 0.75 mm. wide, with the median one-third of
the lancet exposed near the adoral end, but near the
aboral end the lancet is covered by the side plates. There
are 45 side plates in a space of 10 mm. along an ambulacrum.
Th primary side plates are dumbbell-shaped with
one large pore between adjacent plates at the abmedial
margin of the lens-shaped outer side plate, with pores
located along radial and deltoid ambulacral margins. The
surfaces of the basal and radial plates are ornamented
with fine growth lines parallel to plate margins and the
deltoids have aligned granules along growth ridges.
Remarks.—There is regional and stratigraphic variation
among various specimens assigned to this species.
The basal circlet is convex, flat, or slightly concave in
different specimens, and on this basis alone one may
distinguish various species. The object of the present
work is to define genera, and therefore this problem will
have to be considered by later investigators. The variation
in shape of specimens from the St. Louis Group of Illinois
and the Ste. Genevieve Limestone of Kentucky
should be called to attention.
Occurrence.—Mississippian, St. Louis Limestone, Hardin
County, Illinois (syntypes, X-363) and Brown
County, Illinois (E1,498). Ste. Genevieve Limestone,
Crittenden County, Kentucky (1,303). Gasper Formation,
Huntsville, Alabama (71,650). Warsaw Formation,
Florence, Alabama (S3,782).
Types.—Syntypes, X-363, three specimens, one 4-
sided, A. H. Worthen collection, old Illinois State Museum
no. 10,096, now in Department of Geology, University
of Illinois, Urbana. Plesiotype, E1,498, one specimen,
labelled Mesoblastus kirkwoodensis, A. H. Worthen
collection, University of Illinois. Plesiotypes, 1,303, seven
specimens, one polished section, one thin section, and five
EXPLANATION OF PLATE 17
FIGURE PAGE
1-3,7-9. Astrocrinus benniei (ETnERIDGE), plesiotypes, 362,
Harvard Mus. Comp. Zoology, Lower Carboniferous Limestone
Group (shale above no. 2 limestone), Carlops Quarry,
Peebleshire, Scotland; 1,3, oral and aboral views with
"A" ambulacrum toward top of page in fig. / ( X 10.6) ;
2, 9, "C" ambulacral and aboral views of another specimen
(approximately X14), 7,8, aboral and oral views of
specimen with "D" side directed downward ( X17.0) 21
4-6. Pleuroschisma ontario REIMANN, topotype, 35,033, Southworth
coll., Univ. Michigan; Devonian, Hungry Hollow
Formation (coral bed), Ausable River valley northeast of
Arkona, Ontario; oral, "D" ambulacral, aboral views (all
X9.1) 42