K. L. Pre>?derGx\st. 
much helpful advice. The text-figures have been drawn by Dr. D. H. Rayner 
and the photographs prepared by Mr. A. Barlow of the Sedgwick Museum 
and Mr. H, Smith of the University of Western Australia. The author 
gratefully acknowledges her indebtedness to these persons and to many 
others, too numerous to name, who have given her assistance. 
The -work has been done while the author held a Hackett Studentship 
of the University of Western Australia and an 1851 Overseas Scholarship. 
She records here her thanks to the authorities concerned in these awards. 
The publication of this paper has been made possible by a grant from 
the Hackett Studentship Fund of the University of Western Australia. 
The following abbreviations are used in the text : — 
B.M., British Museum (Natural History). 
Aus. Mus., Australian Museum. 
W.A. Mus., Western Australian Museum. 
U.W.A., Department of Geology, University of Western Australia. 
G.S.W.A., Geological Survey of Western Australia. 
The terminology as used throughout this paper is as defined by 
Muir-Wood (1928). All measurements of specimens are given in millimetres 
and the sign -f- after a number indicates measurement along a broken 
specimen. 
XL MORPHOLOGY AND BIONOMICAL INTERPRETATION 
THEREOF. 
External Features. 
The general form of the shells of the Productinae and Strophalosiinae 
is concavo-convex dorso-ventrally. There are, however, some exceptions. 
Within the group Productus sensu lato .the concavity of the brachial 
valve varies from strongly concave as in Krotovia to almost flat as in 
Waagenoconcha. The pedicle valve is always convex and usually strongly so. 
The curvature, as seen in longitudinal profile, may vary but little over the 
whole profile or may change abruptly. In the latter case the shell is called 
geniculate when the curvature has increased and fringed or flanged when it 
has decreased. Fredericks has suggested a classification of the Productids- 
based on the types of visceral cavity produced by the differences in curvature 
of the two valves. He distinguishes three types. 
A. Productus typici a. Pedicle valve with regular cimvature.. 
Brachial valve flat or gently concave. Visceral cavity deep.. 
e.g. Waagenoconcha imperfecta Prendergast. 
B. Productus typici Pedicle valve with regular curvature. 
Brachial valve concave, following the curve of the pedicle- 
valve. Visceral cavity thin. e.g. Krotovia spimdosa 
(Sowerby). 
C. Productus prohoscidei. Pedicle valve regularly curved or 
geniculate. Brachial valve geniculate. Development of 
trail characteristic of the group, e.g. Productus productus 
(Martin). 
