CLASSIFICATION OF THE CHEILOSTOMATOUS 

 BRYOZOA 



By Ferdinand Canu 

 of Versailles, France, 



Ray S. Bassler 

 of Washington, D. C. 



INTRODUCTION 



The Cheilostomata, the highest developed of the five orders of 

 bryozoa, had their origin in the Jurassic rocks of Europe, where they 

 are represented by a few primitive species. By late Mesozoic times, 

 they had expanded into so many species that from then until the 

 present, they remained the predominating order. In the recent seas, 

 the Cheilostomata exhibit the bryozoa at their greatest stage of per- 

 fection and beauty, and this fact in connection with their abundance, 

 has made them the subject of numerous studies. 



Most of the Cheilostomata form most beautiful objects from an 

 artistic standpoint because the frontal wall of the zooecium is com- 

 posed of calcite arranged in most delicate and often bizarre patterns. 

 The earlier classifications of the Cheilostonmta were based upon dif- 

 ferences in these patterns, so that a purely artificial arrangement of 

 genera and families resulted. The calcification of the frontal wall 

 forming these beautiful patterns is, however, only one of the func- 

 tions of the bryozoan and a natural classification must necessarily 

 be based upon all the important functions. Living bryozoa show 

 that, 1, reproduction exhibited in the development of the ovicell and 

 its operculum, 2, the hydrostatic system dealing with the extrusion 

 of the polypide, and 3, calcification and cliitinization or the nature 

 of the skeletal parts of the animal are the essential functions ar- 

 ranged in the order of their importance. Therefore the least impor- 

 tant of these functions was alone considered when so many of the 

 ancient genera and indeed many of the more modern ones were 

 instituted. 



In the course of our work upon the Post-Paleozoic bryozoa, we 

 have devoted much attention to generic discrimination in an endeavor 



No. 2640.— Proceedings U. S. National Museum, Vol. 69, Art. 14. 



3022—27 1 



