ECHINODERMATA - KU ScholarWorks - University of Kansas

108 THE UNIVERSITY OF KANSAS PALEONTOLOGICAL CONTRIBUTIONS
exposed, probably were derived from Troosticrinus, a
Silurian genus. These families are here recognized as
Pentremitidae D ' ORBIGNY, 1852; Troosticrinidae BASS-
LER, 1938; Granatocrinidae FAY, n. fam.; Schizoblastidae
FAY, H. fam.; and Nucleocrinidae BATHER, 1899,
respectively.
The family Pentremitidae, D ' ORBIGNY, 1852, includes
ten genera, of which all have five spiracles
and probably were derived from Hyperoblastus by
complete closure of the sinus. The genus Cordyloblastus
, with four anal deltoids, simple gaps between
side plates, and lancet covered by side plates, was probably
derived from Hyperoblastus. Petaloblastus probably
was derived from Cordyloblastus by outward migration
of the lancet plate and downward migration
of the deltoids, visible in side view, with concurrent
fusion of the cryptodeltoids and superdeltoid into an
epideltoid plate. Another trend from Hyperoblastus
is one toward Devonoblasttts, in which the deltoids
migrate downward, become visible in side view, and
the sinuses are completely closed. This trend leads to
Pentremites in which the lancet moves outward and
one anal deltoid is formed, culminating in Ambolostoma
where five large orals are formed from many
small ones, and to Rho paloblastus, in which the anal
opening moves aborally. A distinct side trend from
Hyperoblastus is one toward Eleutherocrintts, in
which the (D) ambulacrum is shortened and the deltoids
move slightly downward, visible in side view.
Another trend is toward Globo blastus, which probably
was derived from a Devonoblastus that developed a
hydrospire plate and two pores to each side plate as
result of infolds of the ambulacral margins, with reduction
of the hydrospire folds on each side of an
ambulacrum to two. Globoblastus probably gave rise
to Ellipticoblastus by reduction of the hydrospire folds
to a single one on each side of an ambulacrum, and
Ellipticoblastus probably gave rise to Orbitremites by
downward migration of the deltoids over the radials.
From this it can be seen that the hydrospire plate is
probably of little importance in classification and may
develop independently in diverse families. Also, foreshortening
of an ambulacrum has littel value in
higher classification of blastoids.
The family Troosticrinidae BASSLER, 1938 includes
five genera, four of which are closely related. Troosticrinus
is here considered to be a primitive genus that
probably gave rise to other members of this family
by downward migration of the deltoids (Schizotremites),
or to forms oval in shape (Pentremitella), or
conical, with long pelvis and four or five hydrospire
folds (Metablastus), reduced to three, with flaring
pelvis (Tricoelocrinus), or from which came globular
forms with hydrospires reduced to two folds on each
side of an ambulacrum (Diploblastus).
The family Nucleocrinidae BATHER, 1899, was probably
an aberrant off-shoot from Troosticrinus in which
the cryptodeltoids moved outward and downward.
Elaeacrinus, with many oral plates, is inferred to be a
primitive genus from which came Nucleocrinus with
five simple orals, and Placoblastus with six or seven
orals. It is possible that Placoblastus may be an intermediate
genus with the superdeltoid plate exposed,
and Nucleocrinus an advanced genus with the superdeltoid
suppressed. These genera probably did not
give rise to other known genera.
The Schizoblastidae FAY, n. fam. (herein distinguished)
include forms probably derived from a
form similar to Schizotremites, in which the five
paired spiracles form ten spiracles, with anus separate
EXPLANATION OF PLATE 37
FIGURE PAGE
1-3,10. Monadoblastus granulosus FAY, n.gen., n.sp., holotype
(figs. 1-3), paratype (fig. 10), E14,750, Reimann coll.,
Buffalo Soc. Nat. Sci.; Lower Mississippian, Lake Valley
Formation ( ?Nunn member), Lake Valley, N.Mex.; 1-3,
oral, "D" ambulacral, aboral views (all X11); 10, aboral
view of polished cross section with "B" ambulacrum downward
( X9.6) 83
4-6. Tanaoblastus bellatulus (PECK), "hypotype" on label (but
presumed to be holotype), 3,293, Peck coll., Univ. Missouri;
Lower Mississippian, Chouteau Limestone, 9 miles
northeast of Osceola, Mo.; oral, "D" ambulacral, aboral
views of specimen figured by Peck (1938, pl. 26, figs.
1-3) (all X13.1) 102
7-9. Tanaoblastus haynesi (T. H. CLARK), holotype, 347, Harvard
Mus. Comp. Zoology, Mississippian, Madison Limestone,
Squaw Creek, Mont.; oral; "D" ambulacral, aboral
views showing two hydrospire folds on each side of an
ambulacrum and nine spiracular openings around oral
opening (all X6.7) 104
11,12. Carpenteroblastus magnibasis (RowLEy), rnetatype, RX-
22, Robert R. Rowley coll., Univ. Illinois; Lower Mississippian,
Upper Burlington Limestone, Louisiana, Mo.;
//, aboral view of internal mold of specimen figured by
ROWLEY (1901, pl. 28, figs. 22-23) ( X3.9); 12, oral view
of same showing remnant of circumesophagael ring and
pores in deltoids ( X8) 52