View - KU ScholarWorks - University of Kansas

26 The University of Kansas Paleontological Contributions-Paper 99
known only from the Lower Ordovician of
the Soviet Union in strata much younger than
those with other species of Hirsutodontus
(Abaimova, 1972).
HIRSUTODONTUS RARUS Miller
Plate 2, figure 3
Hirsutodontus rarus Miller, 1969, p. 431, textfig.
4H, pl. 64, figs. 36-42; Abaimova,
1972, text-fig. 1; 1975, p. 72, text-fig. 7.10,
pl. 1, fig. 20; LindstrOm, 1973, p. 118, 119,
125; Abaimova and Markov, 1977, P. 91,
pl. 14, figs. 4, 7, pl. 15, fig. 5.
Discussion. - H. rarus apparently evolved
from I-I. hirsutus and differs in having a shallower
basal cavity, a more poorly developed
cusp, and much smaller and more closely
spaced spines. Clavoltamulus elongatus, an
evolutionary descendant of H. rarus, has
granulose ornamentation and virtually neither
cusp nor basal cavity.
Occurrence. -In the United States, Hirsutodontus
rarus is known from throughout the
Cordylodus proavus Zone of Utah (upper
Notch Peak and lower House limestones,
House Range; Miller, 1969, 1978), Nevada
(Whipple Cave Formation, southern Egan
Range), Oklahoma (upper Signal Mountain
Limestone, Wichita Mountains), and Texas
(upper San Saba Member of Wilberns Formation,
Llano uplift). Elsewhere H. rams is
known from East Greenland (upper Dolomite
Point Formation; Miller & Kurtz, 1979), the
Soviet Union (Abaimova, 1972, 1975), and
Australia (E. C. Druce, pers. commun., 1979).
HIRSUTODONTUS SIMPLEX
(Druce & Jones)
Figure 4S; Plate 2, figure 13
Strigaconus simplex Druce and Jones, 1971, P.
98, text-fig. 31, pl. 6, figs. 1-5.
Hirsutodontus hirsutus Miller (part), 1969, p.
431, pl. 64, figs. 27, 28, 32-35 (not figs. 25,
26, 29-31); Jones, 1971, p. 56, pl. 7, figs. 7,
8; Lindstriim (part), 1973, p. 118, 119.3,
121 (not 119.2).
Hirsutodon tus dzherbiensis Abaimova, 1971,
p. 79, text-fig. 4, pl. 10, figs. 9, 10; 1972,
text- fig. 1; 1975, p. 71, text-fig. 7.11, p. 6,
figs. 7, 8; Abaimova and Markov, 1977, p.
91, pl. 14, figs. 8, 9, p. 15, figs. 2, 6, 7.
Hirsutodontus cf. H. hirsutus Abaimova and
Markov, 1977, p. 92, pl. 14, fig. 10.
Discussion. -The relationship between H.
simplex and H. hirsutus is discussed under the
latter species.
Hirsutodontus dzherbiensis Abaimova,
1971, is a large-spined form that LindstrOm
(1973, p. 121) synonymized with H. hirsutus;
however, it is here considered to be a junior
synonym of H. simplex (Druce & Jones),
1971. Druce and Jones' (1971) publication was
issued May 15, 1971, while Abaimova's (1971)
paper is in the October-December, 1971, issue
of the Paleontologicheskiy Zhurnal.
Occurrence. -H. simplex is known in
North America from Utah (lower House Limestone,
House Range; Miller, 1969, 1978),
Nevada (Hales Limestone, Hot Creek Range),
Oklahoma (upper Signal Mountain Limestone,
Wichita Mountains), and Texas (upper
San Saba Member of Wilberns Formation,
Llano uplift). Elsewhere it is known in
Australia (Druce & Jones, 1971; Jones, 1971)
and the Soviet Union (Abaimova, 1971, 1972,
1975; Abaimova & Markov, 1977). In the
United States H. simplex ranges through a
stratigraphic interval of only about 15 m in a
thick miogeosynclinal sequence (Miller, 1978,
table 2). This interval is within the lower Symphysurina
brevispicata Subzone of the Symphysurina
Zone and in the Hirsutodontus
simplex and lower Clavoliarnulus hintzei subzones
of the Cordylodus proavus Zone. The
Australian occurrences are likewise confined
to a thin interval, making H. simplex an excellent
index for international correlation.
Genus MONOCOSTODUS, new
Type species. -Acodus sevierensis Miller,
1969, p. 418.
Description. -Apparatus consisting of
symmetry-transition series with slender, erect
to reclined, simple cones; dextral, sinistral,
and rare bilaterally symmetrical symmetrytransition
variants produced by changes in
position of narrow, sharp costa beginning
near bend of cusp and extending to tip; costa