Permian Productinae and Strophalosiinae of W.A. 
15 
The brachial valve is strongly geniculate. The ornamentation differs 
from that of the pedicle valve only in the absence of spines. The pits, which 
replace the spines on this valve, are not placed opposite them, but appear 
anteriorly. This is particularly noticeable in the row of pits on the sulcus 
separating the ears. No trace of a cardinal area has been observed on this 
valve. 
The interior of the valve is not seen on the syntypes. 
Description of the paratypes — Internal features, — The paratypes show 
the gingiymus more clearly than either of the syntypes. It is divided by a 
wide triangular notch. The cardinal process of the brachial valve projects 
but a little above the level of the hinge as a truncated triangular ridge. 
Internally the muscles of the pedicle valve are those characteristic of the 
genus, longitudinally striated diductors enclosing dendritic adductors, the 
place of insertion of the muscle much thickened. 
Variation within the species. — The topotypes of this species show marked 
variation in the depth of the sulcus between the visceral disc and the ears. 
When the sulcus is shallow and not pronounced the rugae extend on to the 
ears so that these are semireticulate. This ex,tension of the semireticulation 
has an effect on the size of the auricular spines, since where the rugae are 
present the spines are small and similar to those of the visceral disc, these 
replacing the larger spines seen in specimens with a deep sulcus. Recognising 
this as a variation within the species it is then possible to include the two 
forms distinguished by Hosking (1933, p. 46) in the one species. 
A second variable feature of the specimens is the extent of the semi- 
retieulation along the curvilinear length of the shell. Although owing to the 
crushing of many of the specimens it is difficult to determine the original 
shapes, it would seem that rugae are not developed after there is a change in 
the direction of growth, even where this does not amount to a geniculation. 
This relation between the shape of the shell and the ornamentation probably 
Figure 2. 
Cardinal process of D. callytharrensis sp. nov. (x6). 
