ECHINODERMATA - KU ScholarWorks - University of Kansas

BLASTOID STUDIES 93
196
194
195
FIGURES 194-196. Placoblastus obovatus (BARtus), Middle Devonian, Thunder Bay Limestone, near Alpena Michigan
(Buffalo Soc. Nat. Sci., nos. E21,113, E21,115).
194. Cross section of "D" ambulacrum, aboral view (no.
E21,113), X15. 195. Part of "E" ambulacrum,
showing main, inner, and outer side plates (no. E21,115),
X45. 196. Part of "C" ambulacrum, drawn from
polished tangential section (no. E21,115), X45. [Explanation.—Bf,
brachiolar facet; Bp, brachiolar pit; CR, cryptodeltoid;
D, deltoid; ISp, inner side plate; L, lancet; OSp,
outer side plate; P, pore; Sp, main side plate.]
five, each short, 8 mm. long by 7 mm. wide, strongly
recurved in basal concavity, broadly pentagonal in side
view, with short sinus 3 mm. long by 2 mm. wide and
wide tapering deltoid margins 4 mm. long between ambulacrum
and admedial margins of radial plate. Radiodeltoid
suture M-shaped. Deltoids overlap radials.
Deltoids four, broadly lenticular, each 43 mm. long
by 13 mm. wide, with trifold sculpture as in Nucleocrinus,
each ending adorally against an oral plate. On the
anal side at least three anal deltoids are present, a long
central quadrangular hypodeltoid 41 mm. long by 6 mm.
wide, flanked on each side by two lenticular cryptodeltoids
43 mm. long by 3.5 mm. wide. A large hexagonal
plate occurs on the adoral side of the anal opening between
the adorai tips of the cryptodeltoids. This plate
is here interpreted to be a superdeltoid but it could be an
accessory anal oral and the superdeltoid could be below
it, not visible externally. The oral opening is covered by
EXPLANATION OF PLATE 30
FIGURE PAGE
1-9. Nucleocrinus meloniformis (BARais), Middle Devonian,
Hungry Hollow Formation (coral zone of Widder beds),
near Thedford, Ontario. 1,2. Plesiotype, 3,662a, Geol.
Survey Canada; 1, oral view showing five large oral plates
in place (X6.4); 2, "B" ambulacrum showing main and
outer side plates in place but inner side plates missing,
leaving large gaps between side plates (X13).-3.
Plcsiotype, E15,939, Charles Southworth coll., Buffalo Soc.
Nat. Sel.; tile yard, Thedford, Ontario; polished section of
"E" ambulacrum showing inner, outer, and main side
plates (X32).-4. Plesiotypes, E148, Buffalo Soc. Nat.
Sci.; oral view of polished section showing hidden superdeltoid
plate between cryptodeltoids and oral plate on anal
side (X9).-5,6. Plesiotypes, E21,120, Charles South'
worth coll., Buffalo Soc. Nat. Sci.; tile yard, Thedford,
and Hungry Hill, Arkona, Ontario; 5, anal side of spedmen
shown in Pl. 29, figs. 1-3, showing large hypodcltoid
flanked by ridged cryptodeltoids ( X7.8); 6, aboral
view of another specimen (X14.6).-7-9. Plesiotype,
102,707, Charles Southworth coll., U.S. Natl. Mus.; tile
yard, Thedford, Ontario; oral; "B" and "C" combined
ambulacral, and aboral views of pathological specimen
in which the "B" and "C" ambulacra have almost joined
( X 5.1) 86