78 
paleontological geology 
specimens from all sources, that has in part caused the long delay 
in the preparation and publication of this work. For the greater 
part of the delay, however, has been due to the desultory character 
of my studies, arising from causes not within my control. The 
insistent demands of an exacting profession, and the claims of 
business affairs which absorbed the major part of my time, caused 
frequent and often long breaks in the prosecution of the work, 
the total of which must be measured in years. 
“These interruptions, however, have not been without their 
compensating advantages; for during all this time the acquisition 
of new material, chiefly through the medium of collectors in the 
field, has been steadily going on, resulting in important additions 
to our knowledge of this group. And the broader grasp of the 
subject consequent upon this increase of knowledge has enabled 
me to place on a firmer basis certain family divisions, which would 
have been left in an unsatisfactory condition if I had published 
my results a few years ago. 
“I think it only fair to observe further, by way of personal - 
' allusion, that I have labored under the disadvantage of a lack of 
practical zoological training, which compels me to limit my treat¬ 
ment of the subject chiefly to the presentation of the facts from a 
systematist’s standpoint, without venturing too far into the field of 
evolutionary interpretation. This I prefer to leave to others who 
are better qualified to undertake it, and it is my hope that this 
contribution to the sum of knowledge of these organisms may be 
of some service to those who engage in more general discussions. 
“It was evident to me at the outset that the plan of restricting 
the detailed investigation of this group to its American represen¬ 
tatives, as was done in the treatise on the Camerata by Wachsmuth 
and myself, was unsatisfactory. I have therefore endeavored to 
include in this work all known species of Flexibilia.” 
Kkyes. 
