EXPLANATION OF PLATES. 
ALL specimens not otherwise described are in the collection of the Museum of 
Comparative Zodlogy, and all not mentioned as “casts” have the shell present, either 
in part or as a whole. Paul Roetter drew the figures in outline by measurement; the 
author redrew all the specimens using these outlines, but testing the accuracy of the 
measurements before they were finally placed on stone. The outlines in the Summary 
Plates were sketched by the author, and redrawn by Miss Pierson. Unless otherwise 
specified, the figures’ are approximately of natural size, although the process of reducing 
by photography from the enlarged drawings has introduced some slight deviations from 
the measured diameters of the originals. 
