Permian Productinae and Strophalosiinae of W.A. 
3 
The terms suggested by Fredericks serve as useful names for the de- 
scription of visceral cavities, but it is doubtful if they can be used as the 
diagnostic feature by which to distinguish separate genera. The character 
of the visceral cavity may or may not be a reflection of important anatomical 
differences. It is, however, of little importance in modern lamellibranchs as 
Pecten, for example, has one valve (usually the left) flat, while the right 
valve may vary from slightly convex to rotund. There is here, within the 
one genus, a great variation in the size of the visceral cavity. The example 
chosen may not be strictly analogous, however, and where in a large number 
of specimens the visceral cavity is of the same type, this, in combination 
with other features, could certainly be used as a feature of diagnostic im- 
portance. 
In Aulosteges the shell has the same form as in Productus s.l. Where, 
however, the area of the pedicle valve is high and reclined, this valve tends 
to become flattened and the brachial valve is slightly convex, the form 
approaching to the condition seen in the Orthotetince. Among the species of 
Strophalosia the form of the shell does not vary beyond the limits already 
described for Productus s.l. In Etheridgina the pedicle valve is often flat- 
tened by attachment of the whole valve. 
The area of attachment in Strophalosia and Aulosteges raises the ques- 
tion of the position of the shell during life. In Productus s.l. the shell lay on 
the larger pedicle valve with the brachial valve approximately parallel to 
the substratum and the plane of symmetry vertical. The growth of a trail 
allowed the animal to obtain its water supply from a level higher than that 
■of the body. Possibly the shell sank by its weight into the substratum and 
water taken into the body through the trail was cleaner and contained a 
richer food supply. The trail would also serve as a protection to the animal 
in providing only a narrow opening at some distance from the vital organs 
and separated from them by a right-angled bend. In StrojAialosia the point 
of attachment is at the apex of the umbo. It is not known for what period 
of its life the animal was attached, but it seems unlikely, when the small size 
■of the cicatrix is compared with the size of the shell, that this 
condition of growth prevailed throughout life. However, whatever 
the length of this period the shell must have gTown upwards from 
the point of attachment at the umbo. In many Strophalosias, owing 
to the geniculated or bevelled chai’acter of the interior of the brachial valve 
the shell develops a small trail. Presumably, when the shell became too heavy 
to maintain itself in the vertical position it fell on to its heavier pedicle 
valve, the trail then serving as in Productus. An irregular deformation of 
the umbo, presumably due to attachment, is sometimes seen in Aulosteges; 
the same explanation may be offered in this genus. 
The ornamentation of the Productince and Strophalosiince is essentially 
spinose. Spines are developed most frequently on the pedicle valve and 
rarely on the brachial valve which, where the pedicle valve is spinose, de- 
vebps pits corresponding in position to the spines of the pedicle valve. The 
spines may be of one or different sizes, they may be erect, oblique or adherent 
while their position on the shell may vary from genus to genus. They may 
be scattered irregularly or show a definite arrangement such as a row along 
the cardinal margin or separating the ears from the body of the shell. They 
may occur in concentric or radial rows or show a regular quincuncial arrange- 
ment over the whole shell surface. The capacity to develop spines is probably 
