Permian Produotinae and Strophalosiinae of W.A. 
33 
The brachial valve of the genotype A. wangenlieimi (Verneuil) is slightly 
convex over the visceral disc, becoming concave with geniculated margins. 
This valve has an operculiform character throughout this genus, serving as a 
fiattish or slightly concave lid for the visceral cavity. The ornamentation is 
as in the pedicle valve. 
A description of the internal features of a brachial valve of A. wange^i- 
heimi (B.M. BB 32-79) will illustrate the characteristic features of the valve. 
The cardinal process is large and trilobate, it is inserted perpendicular 
to the hinge-line so that it extends horizontally, not vertically as in the Pro- 
ductids. The roots of the cardinal process extend posteriorly, and some part 
of them now lies behind the hinge-line. This is protected externally by a 
triangular extension of the brachial valve which fills the delthyrium of the 
pedicle valve. This structure of the cardinal process is characteristic of 
the genus. 
At its base the cardinal process is continued into two thickened ridges 
which run parallel to the hinge-line, leaving, posterior to them, a rectangular 
platform of which the surface of the valve forms the back and the thickened 
ridge the floor. The development of these ridges varies within the one species 
even under the same environmental conditions; one of the specimens exam- 
ined (B.M. BB 3278) had them enormously thickened (see Figure 4), while 
in another they were but feebly developed with little laterial expansion. In 
the thickened specimen two ridges, directed towards the centre of the shell, 
arise at the base of the cardinal process and unite in the middle line to con- 
tinue forward as the median septum. These two ridges and the lobes of the 
cardinal process form the edges of a diamond-shaped depression which 
separates the cardinal process from the median septum. With less-developed 
ridges the anterior sides of the depression become obscured. 
Figure 4. 
Interior of Bracliial Valve of Aulosteges wangenheimi (Verneuil). Permian. 
Mt. Grebeni, near Orenburg, Russia. B.M. BB 3279 (X3). 
