IX 
UTHORS’ 
T REFACE. 
The Second Part of the Monograph on the Permo-Carboniferous Pelecypoda 
of New South Wales is devoted to an inquiry into the nature and relationship 
of Eurydesma, one of the most interesting Mollnscan types of the Australian 
Permo-Carhoniferons fauna. ^ 
Its somewhat restricted geographical distribution — Tasmania, New 
South Wales, and Queensland, and the Salt Range of India, — its abundance 
in the lower stratigraphical elements of the Permo-Carl)oniferous, and the 
peculiarities of the valve structures, have led to some attention being directed 
to the genus. 
Though diverging greatly in outward form, analogies may he traced 
between Eurydesma^ the Cretaceous 3Iaccoyella, and the recent 3Ieleagrina. 
The umbonal region of the valves in Eurydesma is of extraordinary 
thickness, and it is interesting to note, as Mr. Charles Hedley has pointed 
out, that all recent bivalves comparable in valve thickness occur in tropical 
waters. 
The specimens in the collections of the Mining and Geological Museum, 
the Australian Museum, the Technological Museum, and the University of 
Sydney have been made use of, and we have to express our indebtedness to 
the authorities of the various institutions for cordial assistance. 
The Plates have been drawn by Mr. A. R. McCulloch, of the Australian 
Museum. 
B 
