Permian Productinae and Strophalosiinae of W.A. 
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Brachial valve concave, lamellar tending* to nodular structure. Area 
and pseudo-chilidium relatively larg-e. Cardinal process inclined almost to 
horizontal; muscle impressions small at base of cardinal process. 
Description . — The pedicle valve is firmly affixed to the underlying shell 
in most cases and hence the ornamentation is not known. In one specimen 
(Aus. Mus. P 38498) the shell is geniculate and the trail is ornamented by 
hne concentric lamellae and stout oblique spines. The area is wide and flat, 
in length half the width of the valve and with a width one-flfth of the length. 
The area is marked by longitudinal striations, interrupted medially by a 
triangular deitidium. 
The cardinal margin bears very long, slender spines which are cemented 
to the host. These have a length much greater than the length of the shell, 
one spine extending 1.3 cm. from the margin. The spines occur in a matted 
group on the ears becoming more sparse towards the umbo ; they arise 
perpendicular to the cardinal margin. 
The teeth are strong, hollowed posteriorly to give a semi-ovoid cavity, 
and diverging. The muscle impressions take a tetrahedral form, one apex 
of the tetrahedron towards the umbo and beneath the area. The muscular 
apophyses are slightly concave, they appear smooth and divided into a 
greater and a lesser part by a narrow ridge parallel to and near their 
anterior margins. The edge separating them is a thickened ridge simulating 
a median septum. The anterior face of the tetrahedron is narrow, and has 
■curved side edges, due to the concavity of the apophyses. Any other mark- 
ings on the inside of the shell have been obliterated. 
The brachial valve has the shiny lamellar structure characteristic of so 
many Stroplialosias. Superimposed on these lamellae are concentric ■wrinkles 
extending over the entire surface of the valve. The wrinkles are irregular 
in intensity giving a general impression of a nobbly rather than a lamellai 
structure. It is possible, although no evidence of their presence can be seen 
on this specimen, that spines were developed over part of the visceral disc. 
Marginal spines were present as shown by the numerous pustules. The 
brachial valve is swollen below the umbo into a strongly convex semi- 
spherical region which, undergoing rapid change of curvature, becomes flat 
and so continuing across the visceral disc upturns marginally. The area of 
the valve has a width about half that of the pedicle area : the chilidium is 
triangular. If the valves are held in such a position that their height is 
\ertical, the areas of both valves are in one horizontal plane. 
Figure 9. 
Cardinal Process of Etheridgina muirwoodae n. sp. (Xfi). 
The cardinal process is relatively large and is inclined almost at right 
angles to the area of the valves. It shows a characteristic trifld structure when 
viewed ijosteriorly, although the lateral arms adhere closely to the central 
