PRELIMINARY REMARKS. 15 
poorness of the material at hand, which, although sufficiently perfect to be 
readily distinguished by a practiced eye familiar with the associated forms, is 
not good enough to permit figures of them to be made which would enable 
others to identify them. Consequently this monograph can not be said to 
be entirely complete. 
In dealing with the different species and genera previously described, 
I have endeavored to ascertain their true nature as far as possible from 
the type specimens when they could be found, and have adopted them 
wherever it seemed reasonable. Comments on many of them will be found 
in the text of the volume, where I give my reasons for adopting or rejecting 
them. 
