Permian Productinae and Strophalosiinae of W.A. 
37 
The brachial valve is fiat and is without an upturned margin. The 
median septum crosses two-thirds of the length of the shell. The surface of 
the valve is roughened by weathering, but numerous pits indicate the former 
presence of spines. 
A much larger specimen, F 37710, is a pedicle valve with a high undis- 
torted area. The valve has the same recurved margin and ornamentation as 
seen in the type. The median sinus is well-developed anteriorly, but is faint 
on the visceral portion of the shell. The area is wnde and longitudinally 
striate; the pseudo-deltidium is narrow, parallel-sided and bears nodular 
perforated tubercles; it is short, continuing for only half the width of the 
area so that a large open space occu])ies the centre of the cardinal margin 
(filled, when the brachial valve is in position, by the triangular extension 
of the cardinal margin). This specimen differs from the type in size and 
in the possession of deltidial spines. Although no intermediate forms are 
known it is im])ossible to separate the specimen on those grounds alone. 
The deltidial spines are rarely present in species of Aulosteges and their 
absence may be due to removal by weathering rather than to a difference in 
development. 
Bey^iar'ks . — The distinctive feature of this species is the sharp recurving 
of the area, a feature not seen in other species of the genus. 
The a]^pearanee of a larger shell with the same characteristics as those 
described for Aulosteges spinosus nullifies the suggestion of Hosking (1931^ 
p. 19) that this species was possibly only the young form of Aulosteges ingens 
Hosking, 
STROPHALOSIA King 1844. 
1844. — King, Ayu). Mag. Nat. Hist., XIV, p. 318. 
Gniotiipe. — OrihU-' cxcavata Geinitz, Ueber einigc Petrefacte des Zeclisteins 
iiiul Miiscdielkalk's. .V. Jh. Min. Geol. Falllont. 1842, p. 578 Taf. x hgs. 12, 13. 
Diagnosis. — Small to medium-sized shells. Concave to platy-convex dorso- 
ventrally with Avell-developed areas on both valves. Umbo distorted by cica- 
trix of attachment. Ornamentation essentially lamellar, lamellae usually 
interrupted by spines on pedicle valve; spines rarely present on brachial 
valve. 
Pedicle valve with teeth litting into sockets of bachial valve. Brachial 
valve Avith median septum, non-dendritic muscular impressions and pro- 
nounced brachial impressions. Trifid cardinal process well-developed. 
Description. — The members of the genus Strophalosia are never large 
shells; they vary in shape from longitudinally to transversely oval, with the 
hinge-line equal to or slightly less than the greatest Avidth of the shell. The 
pedicle valve is usually evenly convex, rarely geniculate. The brachial valve 
is, however, usually geniculate, being flat or concave in the visceral portion 
AA’ith upturned lateral and antenlor margins. Both valves possess a distinct 
area, that of the pedicle \'alve being the larger. There is no ojmn delthyrium, 
a pseudo-deltidium being ahvays present. 
Strophalosia' has been described as a spinose Productid with an area. 
This description is, hoAvever, a little restricted, as all species of Strophalosia^ 
for example Strophalosia kimberlcgemis mihi, do not possess sjunes. The 
characteristic of the ornamentation is rather its lamellar structure. The 
lamellae are usually distinct, their outer surfaces and edges forming the ex- 
ternal shell surface. This distinctness of the lamellae indicates that in the 
