Revision of Lithostrotionella - USGS

SYSTEMATIC PALEONTOLOGY 27
Petalaxis bailliei (Nelson)
Lithostrotionella bailliei Nelson, 1960, p. 114, pl. 21, figs. 7, 8; 1962,
pl. 14, figs. 1, 2.
Lithostrotionella cf. bailliei Nelson. Bamber, 1961, p. 126, pl. 10, figs.
la-g.
Diagnosis. -Petalaxis with corallites 5 to 6 mm in
diameter and 17 to 18 major septa that ordinarily extend
to the columella but seldom extend into the dissepimentarium.
Minor septa ordinarily well developed. Columella
a simple thickened axial rod or plate formed by
extension of the counter septum. Dissepimentarium
composed of a single row of large inflated dissepiments.
Tabulae ordinarily complete, essentially horizontal, and
irregularly spaced 3 in 1 mm. Ratio of tabularium width
to corallite diameter about 0.5. Mode of increase
unknown.
Description of holotype.- See Nelson (1960).
Discussion. -This species is distinguished from P.
wyomingensis and P. tabulatus by its smaller corallite
diameter.
Occurrence.- Lower Carboniferous, Visean. Mount
Head Formation, Alberta, Canada; and Prophet Formation,
British Columbia, Canada (E. W. Bamber, written
commun., 1980).
Petalaxis tschucoticus (Onoprienko)
Lithostrotionella tschucotica Onoprienko, 1976, p. 30, pl. 10, fig. 6, pl.
11, figs. 1, 2.
Diagnosis.-Petalaxis with corallite diameter 5 to 7
mm and 15 to 17 major septa that ordinarily extend to
the columella but seldom extend into the dissepimentarium.
Minor septa poorly developed. Columella a simple
axial plate connected to cardinal and counter septa.
Dissepimentarium composed of a single row of large inflated
dissepiments. Tabulae ordinarily complete,
horizontal, commonly turned up at columella, regularly
spaced 0.3 to 0.5 mm apart. Ratio of tabularium width to
corallite diameter about 0.5 to 0.6. Mode of increase
unknown.
Description of type material.~ See Onoprienko (1976).
Discussion.-This species differs from P. bailliei by
having fewer major septa, a less robust columella, and
weaker minor septa.
Occurrence.- Lower Carboniferous, Namurian.
Yunon Suite, West Chukotka, U.S.S.R.
Petalaxis flexuosus species group
Petalaxis flexuosus (Trautschold)
LithostTotionjlexuosum Trautschold, 1879, p. 37, pl. 5, figs. 7a, b.
Lithostrotionella jlexuosa (Trautschold). Dobrolyubova, 1935a, p. 11,
pl. 3, figs. 1, 2; 1935b, p. 18, pl. 3, figs. 1, 2.
?Lithostrotionellaflexuosa (Trautschold). Heritsch, 1939, p. 30, pl. 13,
fig. 5, pl. 19, fig. 5.
?Lithostrotion [Lithostrotionella] jlexuosum Trautschold. Bassler,
1950, p. 235.
Diagnosis.-Petalaxis with corallite diameter 5 to 7
mm and 14 to 17 major septa that approach t~e columella
but seldom reach it and commonly extend into
the dissepimentarium. Minor septa well developed. Columella
a simple thickened axial plate ordinarily connected
to the counter septum and to the cardinal sep~m
in some corallites. Dissepimentarium composed of 1 to 2
rows of generally small inflated dissepiments of varying
sizes. Tabulae complete and incomplete, horizontal to inclined,
nat, concave or convex, irregularly spaced 0.25
to 1 mm apart. Ratio of tabularium width to corallite
diameter 0.6 to 0.7. Mode of increase unknown.
Description of type material.- See Trautschold (1879).
The diagnosis is taken largely from Dobrolyubova's
(1935b) descriptions and illustrations of topotypes.
Discussion. - Petalaxis flexuosus differs from P.
stylaxis by lacking a complex columella and by having
better development of the minor septa, more extensions
of the major septa into the dissepimentarium, and
generally smaller dissepiments.
Fomiehev (1953, p. 453) and Kozyreva (1974, p. 25)
plac·ed P. flexuosus in the synonymy of P. mac_co¥an_us
Milne-Edwards and Haime because of general similarity
in morphology. I regard these , two species as distinct
because P. flexuosus does not seem to have axial tabellae
like P. maccoyanus. However, Sutherland (1977, p. 187)
pointed out that the complexity of the axial structure is
a variable feature in topotypes of P. maccoyanus; hence,
Dobrolyubova's (1935b) description may be based on
simple corallites in a variable colony.
Heritsch's (1939) specimen is referred questionably to
the species because no longitudinal section is available.
Occurrence.- Middle Carboniferous, Moscovian.
Myachkovo Horizon (C
4
2 ), Moscow Basin, U.S.S.R.
Kings Bay, Spitzbergen(?).
Petalaxis donbassicus (Fomichev)
Lithostrotionella donbassica Fomichev, 1939, p. 60, pl. 9, figs. 4a, b.
Lithostrotion [Lithostrotionella] donbassica (Fomichev). Bassler,
1950, p. 222.
Diagnosis. -Petalaxis with corallite diameter 5 to 7
mm and 14 to 17 major septa that approach the columella
but seldom reach it and commonly extend into
the dissepimelitarium. Minor septa well developed. Columella
a strongly thickened axial plate ordinarily connected
to the counter septum. Dissepimentarium com-
. posed of 1 to 2 rows of inflated dissepiments of varying
sizes. Tabulae ordinarily complete, horizontal, irregularly
spaced 0.25 to 0.5 mm apart. Ratio of tabularium
width to corallite diameter 0.5 to 0.6. Mode of increase
unknown.
Description of type material.-See Fomichev (1939).
Discussion.-This species is very similar to Petalaxis
flexuos1.tS, from which it differs in having better develop~