62 
N. W. ARCHBOLD 
Strophalosia jimbaensis Archbold 1986: 102-104, 
fig. 2A-G. 
Strophalosia sp. cf. S. jimbaensis .—Archbold 1986: 
104, fig. 2H-0. 
Material. GSWA F4383 5-438 50, two natural ferrugi¬ 
nous casts of dorsal valve exteriors, five external 
moulds of ventral valves, one internal mould of a ven¬ 
tral valve, one natural cast of a ventral valve interior 
and seven internal moulds of dorsal valves, all from 
GSWA locality 94217, Billidee Formation, collected 
by Dr S. K. Skwarko, Geological Survey of Western 
Australia. 
Size ranges . Maximum width 25.4-40.2 mm; hinge 
width 19.2-28.2 mm; ventral length 20.6-29.4 mm; 
dorsal length 19.6-32.6 mm. 
Diagnosis. Medium to large sized Strophalosia 
with moderately convex ventral valve and con¬ 
cave dorsal valve. Dorsal valve with well defined 
dimples, growth lamellae and radial capillae, no 
spines. Ventral valve with hinge spines, two 
rows on ears, numerous scattered suberect body 
spines and a shallow median sulcus or flatten¬ 
ing. 
Comments. Dickins (in Konecki et al. 1958: 33) 
was the first to recognise “ Strophalosia nov. sp., 
resembling a species from the Callytharra For¬ 
mation” in the basal One Gum Formation as¬ 
semblage. Eight specimens from the assemblage 
were figured by Archbold (1986, fig. 2F1-0) who 
compared them with the Jimba Jimba Calcare- 
nite species Strophalosia jimbaensis. Different 
styles of preservation between the type speci¬ 
mens of S. jimbaensis and the One Gum speci¬ 
mens prevented unequivocal assignment of the 
latter to S. jimbaensis. 
The well preserved new suite of specimens 
from the Billidee Formation serves to unite the 
two collections discussed above and provides 
additional information on details of the ventral 
exterior spines and the dorsal interior and car¬ 
dinal process. Spines on the ventral ears are in 
two rows and curve back towards the umbo; they 
are in excess of 8.5 mm in length. Body spines 
are in rough concentric rows and project lat¬ 
erally and anteriorly near the exterior perimeter 
of the ventral valve. The dorsal interior pos¬ 
sesses a thin median septum about half the valve 
length at submaturity, but at maturity a thick¬ 
ened median septum is some two-thirds the 
valve length. Large brachial ridges become 
prominent at full maturity. The cardinal process 
is relatively small, bilobed internally and spike¬ 
like at submaturity when it projects posteriorly 
beyond the hinge line of the dorsal valve. At 
maturity, the cardinal process is broader and 
more massive, approaches a quadrilobed state 
internally and projects internally in the plane of 
the dorsal interarea. 
Several other species of Strophalosia have 
been described since the erection of S. jimbaen¬ 
sis by Archbold (1986). Strophalosia perfecta 
Waterhouse & Rao (1989) from the Early Per¬ 
mian of the Bap Formation, Rajasthan is a much 
smaller species than 5. jimbaensis , suggesting 
comparison with the Western Australian Sterli- 
tamakian species S. irwinensis Coleman (see 
Archbold 1986). S. concentrica Clarke, 1990 
from the Early Permian of Tasmania is a distinct 
small to medium sized globose species that does 
not warrant close comparison with S. jimbaen¬ 
sis. S? vollosovitschi (Fredericks, 1931) as 
recorded by Abramov & Grigor’eva (1988:104, 
pi. 1, figs 23-25, pi. 2, figs 1, 2, 7) from 
Verkhoyan’ya, northeast Siberia is a large spe¬ 
cies apparently lacking distinct dorsal external 
dimples. 
Strophalosia is a characteristic genus of the 
Early Permian (Asselian-Sakmarian) of Aus¬ 
tralia (Archbold 1986, Clarke 1990) although 
ranging younger in Western Australia with the 
species S. jimbaensis. The genus is unknown in 
the well known Baigendzhinian faunas of the 
Carnarvon and Canning Basins, although a very 
rare species (2 specimens?) is known from the 
early Baigendzhinian fauna of the Mingenew 
Formation of the Perth Basin (Archbold 1988). 
The Mingenew species possesses distinctive 
smaller dorsal exterior dimples than those of S. 
jimbaensis. 
Superfamily Aulostegacea Muir-Wood & 
Cooper, 1960 
Family Aulostegidae Muir-Wood & Cooper, 
1960 
Subfamily Aulosteginae Muir-Wood & 
Cooper, 1960 
Genus Aulosteges von Helmersen, 1847 
Type species. Orthis wangenheimi de Verneuil, 1845 
(= Aulosteges variabilis von Helmersen, 1847). 
Aulosteges sp. 
Fig. IE 
Comments. A single natural cast of the exterior 
of a dorsal valve (CPC 24505) from BMR local¬ 
ity WB 9, basal One Gum Formation, indicates 
the presence o f Aulosteges s.l. in the assemblage, 
on the basis of its distinct, low dorsal median 
