A SYNOPSIS OF AMERICAN FOSSIL P.RYOZOA. 



By John M. Nickles and Ray S. Basslek. 



INTRODUCTION AND ACKNOWLEDGMENTS. 



So voluminous has the literature of natural history ]>ecome that the 

 workers in any special branch, and the general student as well, feel the 

 need of compilations showing what has been done. This need, keenly 

 felt in our study of the fossil bryozoa, compelled us to begin such a 

 compilation some years ago. This we now place at the service of our 

 fellow-workers with the hope that it may lighten the labors of the 

 systematist and open the way for an enlarged use of the bryozoa in 

 stratigraphy. 



The bryozoa are generally admitted to be one of the most difficult 

 groups of fossils. They are often of small size and can seldom be 

 determined by the unassisted eye. Their accurate discrimination 

 necessitates tedious study. Few have cared to give this. Because, 

 also, great uncertainty has prevailed as to what constitutes classifica- 

 tory characters, a large amount of confusion and synonymy cumbers 

 the literature of the subject. Thus the study of the bryozoa has 

 become doubly repellent. 



The extended investigations of the structure of fossil bryozoa made 

 b}^ Mr. E. O. Ulrich, following in the lines pioneered l)y Dr. H. 

 Alley ne Nicholson, have shown that we can not be sure of the position 

 of any form in the scheme of classification until we have learned its 

 internal structure by means of thin sections examined microscopically. 

 This mode of investigation is difficult and tedious, but our studies have 

 convinced us that a knowledge of internal characters is absolutely 

 essential to a correct understanding of phylogeny and systematic 

 position. 



As but few authors have described the internal structure of their 

 species, and as those who have given descriptions have not alwa3's had 

 a clear understanding of what is essential in the appearance presented 

 by thin sections, it is not possible to be sure of the generic placement 

 of a large number of species. Some authors have referred species to 

 genera to which we are certain they do not belong; but as enough has 

 not been made known of such forms to enable us to refer them to other 



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