STUDIES ON THE CYCLOSTOMATOUS BRYOZOA 



By Ferdinand Canu 



Of Versailles, France 



AND 



Ray S. Bassler 



Of Washington, District of Columbia 



The present paper is our second contribution to the above subject, 

 the first having been pubhshed in 1922^ under the subtitle of "Fossil 

 and Recent Parallelata and Rectangulata." As explained in this 

 first paper, our efforts are especially directed, first, to the study of the 

 internal structure of these organisms by means of thin sections in 

 order to determine the method of gemmation and the occurrence and 

 structure of the various kinds of tubes, and, second, to the function 

 of reproduction as brought out by the ovicells. Cyclostomatous 

 bryozoa are extremely abundant in certain Mesozoic rocks; indeed, 

 they form almost the entire bryozoan fauna of most formations 

 before the Upper Cretaceous. 



2. LOWER CRETACEOUS CYCLOSTOMATOUS BRYOZOA 



The Cretaceous Cyclostomata have received attentiom from many 

 authors, but particularly through the work of D'Orbigny in volume 

 5 of the Paleontologie franpaise and Gregory in his two volumes of 

 the Catalogue of the Cretaceous Bryozoa in the British Museum. 

 Both of these authors, in fact most previous students, have adoped 

 an artificial classification which in the number of genera proposed 

 and the slight reasons for their existence is amazing. Gregory's two 

 volumes are valuable contributions to the bibliographic and histori- 

 cal sides of the subject and his studies of the internal structure mark 

 a great advance in the science. Our studies carry Gregory's efforts 

 still further; in fact, our main object has been an effort to determine 

 the natural generic characters in this group. 



We have undertaken the study of the Lower Cretaceous Cycloato- 

 mata at this time due to our possession of ample, well-preserved 



1 Proc. U. S. Nat. Mus., vol. 61, pp. 1-160, 28 pis., 40 text flgs. 



No. 2593.— Proceedings U. S. National Museum. Vol. 67, Art. 21. 



53648—26 1 1 



