400 University of California Publications in Zoology [Vol. 18 



Acknowledgments 



In working on this subject the writer has been very greatly in- 

 debted to Professor Charles A. Kofoid, of the Department of Zoology 

 of the University of California, for the generous use of his personal 

 library and material, and for direction and advice at eveiy stage, 

 without all of which this work would have been quite impossible. 

 The writer is also indebted to the Scripps Institution for Biological 

 Research at La Jolla, California, for making extensive special collec- 

 tions at sea on two different occasions, and for the privilege of exam- 

 ination of other collections of the Institution, and also to the members 

 of the staff* of this Institution for advice upon the problem and 

 assistance in making the collections. The United States Bureau of 

 Fisheries has courteously permitted the examijiation of plankton col- 

 lections made by the U. S. S. "Albatross" in San Francisco Bay and 

 along the coast of the Pacific states, Alaska, and Japan. Additional 

 material has been furnished by Professor John F. Bovard, of the 

 University of Oregon ; by Professor Seitano Goto, of the University 

 of Tokyo ; by the Oceanographic Institute of Monaco ; by the Biolog- 

 ical Station of Cette ; by the Port Erin Biological Station ; and by the 

 Naples Zoological Station. For the privilege of applying this material 

 to the problem in hand the writer wishes to acknowledge his gratitude. 

 Appreciation is also expressed for the privilege of using from Profes- 

 sor Kofoid 's unpublished work for purposes of comparison a large 

 number of original and as yet unpublished drawings of Peridinidae 

 made by Miss Viola M. Bathgate under his direction. 



Relationships and Morphology of the Dinoflagellates 



The Dinoflagellata form a part of that group of Protozoa, the 

 Mastigophora, which are characterized by possessing during the 

 greater part of their life cycle specialized organs of locomotion in the 

 shape of one or more flagella. Except, however, for similarities in the 

 form of the locomotor apparatus the Mastigophora present little else 

 in common, and the several groups brought together in this class often 

 show closer relationships in other respects to groups outside this class, 

 such as the Bacteria, Rhizopoda, and Ciliata, than to each other. 

 Classification according to the number of flagella is, therefore, some- 

 what arbitrary. The Dinoflagellata, however, which are defined not 

 only by the possession of two flagella, but also by having a shell of 

 material similar to cellulose in texture and in chemical composition. 



