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32 The University of Kansas Paleontological Contributions-Paper 99
sessing a thin layer of apatite that covers a
massive white basal cone. The white basal
cone of this new species is virtually identical
to the entire white element of associated Prooneotodus
rotundatus, and a homology is
strongly suggested between the basal cone of
the former and the entire element of the latter.
Proconodontus tenuiserratus, n. sp., differs
from the new species only in possessing a
small, faintly serrate posterior keel. The
evolutionary relationships among these three
kinds of elements may be clarified by histological
investigations now in progress.
Proconodontus tenuiserratus is the
ancestor of P. posterocostatus, which differs
in having a more developed and nonserrate
posterior keel. Two paratypes of Coelocerodontus
burkei Druce and Jones (1971, text-fig.
22e, pl. 11, figs. 5, 6) are reassigned to this
species. Elements in my collections from the
Black Mountain section of Druce and Jones
(1971) are identical to those from Texas.
Occurrence. -In the United States P.
tenuiserratus is known from Texas (149 elements
from upper Point Peak and lower San
Saba members of Wilberns Formation, Llano
uplift) and Oklahoma (three elements from
the Fort Sill Limestone, Wichita Mountains).
These elements are from the upper Ellipsocephaloides
Zone in Texas and from the
coeval upper Saratogia Zone in Oklahoma,
both of late Franconian age. The species is
also known from Australia (Druce 8,z Jones,
1971).
costa on one side, resulting in dextral and
sinistral forms; broad groove often present
posterior to costa. Basal cavity moderately
deep; white basal cone often prominent. Most
of cusp composed of white matter.
Discussion. - Serniacontiodus Miller was
originally described as a subgenus of Acontiodus
Pander. It was raised to genus rank by
LindstrOm (1973, p. 437), and is recognized as
such here. LindstrOm (1973) assigned several
species described by Miller (1969) to this
genus, including two described under different
generic names. Because of different apparatuses,
these latter species are reassigned
here as Monocostodus sevierensis (Miller) and
Utahconus utahensis (Miller).
Semiacontiodus is probably the ancestor
of Acoritiodus Pander, judging from similarity
of the symmetrical elements; however, the
apparatus of Acontiodus is unknown. Acontiodus
elements have shallower basal cavities
than do Semiacontiodus elements, and in
Acontiodus, white matter is confined to a
growth axis instead of comprising nearly the
entire cusp as in Semiacontiodus.
Semiacontiodus bicostatus Miller, 1969,
was described from broken elements. Subsequent
collecting has not produced complete
elements that can be surely assigned to this
species. It is regarded here as an unrecognizable
species and is not further considered.
SEMIACONTIODUS NOGAMII Miller
Genus SEMIACONTIODUS Miller, 1969
Type species. -Acontiodus (Serniacontiodus)
nogamii Miller, 1969, p. 421; by
original designation.
Emended diagnosis. -Apparatus a symmetry
transition of two types of erect to reclined
simple cones; symmetrical elements
more diagnostic but much less abundant than
asymmetrical elements; anterior sides of both
elements lacking costae or keels. Symmetrical
element slightly compressed anteroposteriorly;
lateral or posterolateral costae on both
sides; posterior costa may be present; fine
striae covering well-preserved elements.
Asymmetrical element round to oval at base,
base may be slightly expanded posteriorly;
Figure 4V, W; Plate 2, figures 10-12
Acontiodus (Semiacontiodus) nogamii Miller,
1969, p. 421, text-fig. 3G, pl. 63, figs.
41-50; 1971, text-fig. 17A, pl. 1, figs. 1-4.
Semiacontiodus nogamii Lindstr6m, 1973, p.
441-443.
Acodus housensis Miller, 1969, p. 418, textfig.
3A, pl. 63, figs. 11-20; Jones, 1971, p.
43, pl. 3, fig. 6.
Oneotodus datsonensis Druce and Jones
(part), 1971, P. 80, pl. 14, fig. 4 (not figs.
1-3).
Oneotodus erect us Druce and Jones, 1971, p.
80, text-fig. 26d, pl. 15, figs. 2-9; Jones,
1971, p. 57, pl. 3, fig. 8, pl. 8, fig. 8.
Oneotodus variabilis Abaimova and Markov,
1977, p.93, pl. 14, fig. 11, pl. 15, fig. 4.