EXPLANATION OF PLATES. 



Plates I — IV, VII and VIII are intended to be a further elucidation 

 of the text, especially as to shell structures. Plates III and IV are compara- 

 tive representations of the beak sculpture and marsupial characters of the 

 three Sub-Families. Plates V and VI are careful drawings of new species 

 described and figured for the first time. Plate IX shows physiological 

 relations while Plates X — XIV show the ecologic. Plates XV — XXVIII 

 are photographs of shells representing about one-half natural size, arranged 

 in progressive order of classification, and, in most cases, the shell structures 

 of the exterior are shown by the left valve and of the interior by the right. 



