Permian Productinae and Steophalosiinae of W.A. 
51 
pseiido-deltidium which is not raised above the general surface of the area. 
Only one tooih has been seen ; this is large and rounded with the concavity 
towards the lateral border. 
The umbo is not prominent, having been absorbed by the cicatrix of 
attachment; this is small and usually almost perpendicular to the surface of 
the area. 
The brachial valve is unknowm. 
Reynarks. — Within this species there is a large variation in shape, many 
of ihe shells becoming elongated. It is noticeable that in this species, as in 
many Strophalosias (e.g., S. kunherleifetisis mihi) the shells appear very 
narrow’ in the hinge region when seen as an internal cast. This is due to the 
very close fitting ears which leave almost no space between those of the two 
valves when these are in contact. 
Comparisoyi with other species. — This species is characterised by the 
regularity of the spines over the body of the shells, the spine groups on the 
ears, the small regular point of attachment and the absence of lamellar 
structure. It approaches nearest to 8. tenuispina Waagen from w’hich it 
may be distinguished by the much coarser spinosity of that species and the 
larger size of S. ynultispinifera. 
STROPHALOSIA sp. A. 
PI. vi, fig. 10-12. 
Material, — I'.W.A., 20448 Fossil Cliff, Iiwin Kiver District. Fossil Cliff 
horizon. 
Diagnosis: — Shell longitudinally oval in outline, evenly curved both 
transversely and longitudinally. Hinge-line less than greatest wndth of shell. 
Ornamentation of lamellae wnth fine adherent spines concentrically arranged. 
Pedicle valve sw’ollen, non-geniculate, sides sloping steeply. Area narrow, 
triangular. Small divergent teeth. 
Brachial valve unknowm. 
Description. — A single jmdiele valve from the Iiwvin River District show’s 
distinctive characters. 
Dimensions. 
Height 
11.9 
Maximum width . . 
11.6 
Length of hinge-line 
6.8 
Length of jTedicle valve 
18.6 
The valve is swmllen w’ith the hinge-line less than the greatest w’idtli of the 
shell : the shell is w’idest near the anterior margin. The umbo is completely 
obliterated by a large scar of attachment, it has become incurved so that 
the area now’ faces antero-dorsallv. The spines are regularly arranged in 
concemtric row’s and are all of equal size, there being no sign of a secondary 
series of siunes as occurs in so many of the Indian forms. The rows are 
widely separated and between them are the silky laminations of the shell 
structure. 
The area is well-develoned w’ith a wdde delthvrium: the teeth a*-^ lar^re 
and diverging. The muscle impressions are high in the valve. The adductors 
are central, separated bv a median ridge and enclosed on the outside by the 
diductors, which are flabellate and ]moduced anteriorly. 
