UNIVERSITY OF CALIFORNIA PUBLICATIONS 



ZOOLOGY 



Vol. 6, No. 12, pp. 225-284, Pis. 18-25 December 31, 1910 



THE CYCLOSTOMATOUS BRYOZOA OF THE 

 WEST COAST OF NORTH AMERICA. 



BY 



ALICE ROBERTSON. 



This paper is the third of the series by the writer treating 

 of the bryozoa of the Pacific coast of North America, and 

 includes the Cyclostomata found in the present collections of the 

 University of California and the University of Washington. 



The sub-order Cyclostomata is characterized by great sim- 

 plicity of structure. The zocecia are calcareous tubes with circular 

 apertures, but without accessory markings, or appendages, such 

 as we find in the Chilostomata. This very simplicity of structure 

 makes it difficult to find suitable taxonomic characters. Waters 

 ('84), in his discussion of the classification of the fossil 

 Cyclostomata, mentions the importance of the ovicell as a diag- 

 nostic mark, but regrets its frequent absence, or mutilation 

 anions' fossils. Fortunately, among recent and living 

 Cyclostomata, the ovicells, or orecia, are frequently numerous, 

 and when they are present they form a satisfactory character 

 because of their constancy of form. Harmer ('91, '96, '98) has 

 used the shape and position of the ocecium, and especially of its 

 aperture, to determine the species of three large genera of the 

 Cyclostomes: Crisia, Tubulipora, Lichenopora. This method has 

 proved most satisfactory in identifying the present collection. 

 and ooecial characters have been used as far as possible in the 

 determination of all species. It remains true, however, that in 

 some cases when ocecial characters were not available, characters 

 which are considered less stable have been used. Thus, in 

 Idmonea, Entalophora, Mesenteripora and Heteropora, mode 



