BRYOZOA. 287 



PREFACE 



For reasons pointed out in my letter of transmittal, the pre- 

 sent work falls considerably short of being a "Monograph" of 

 the Palaeozoic Bryozoa of Illinois, and much umvrought material 

 still remains in the State Museum. Many new and important 

 forms are also contained in private collections, while in my 

 own there are over two hundred Palaeozoic species (many of 

 them from Illinois) that must await opportunities for publica- 

 tion. This, however, was not so much a cause for regret as the 

 loss of much time that was consumed in selecting just such 

 forms as would show the characters and limits of the genera in 

 the best manner. My desire to establish the generic divisions 

 in such a manner that they would readily appeal to the mind 

 of the student I sought to fulfill by incorporating into the re- 

 port as many diagnostic species as possible. On this account 

 the plates, especially the latter ones, are more crowded, and 

 some of the species less fully illustrated, than I had originally 

 intended. The crowded condition of the plates, on the other 

 hand, bears witness to the fact that I have done what I could 

 in the way of illustration, and in most cases, I have no doubt, 

 it will be found to suffice for present needs, or until a "Mono- 

 graph" of the Palaeozoic representatives of the class can be 

 prepared. 



Palaeontologists have now universally conceded that in the 

 determination of such difficult groups of organisms as the fossil 

 Bryozoa the microscopic structure is the most essential ele- 

 ment. The superficial characters may vary greatly in differently 

 preserved specimens, or they may not be recognizable, while 

 the mere external form or habit of growth is too treacherous a 

 guide to be relied upon. The older palaeontologists, without 



