INTRODUCTION 



water with temperatures as low as 15° and 16° C off 

 Japan, off California, and in the southeastern Pacific. 

 In the Atlantic it was found near the British Isles in wa- 

 ter with temperatures as low as 12 °4 C. It was un- 

 doubtedly carried there in the North Atlantic West Wind 

 Drift. Thus, this species is an excellent indicator of 

 the intrusions of tropical water masses. 



It was a notable fact that while the temperature 

 conditions appeared to regulate the distribution of many 

 species, no correlations could be found between the 

 chemical composition of the water and these distribu- 

 tions. The most striking result obtained in regard to 

 the relation between the chemical conditions and specif- 

 ic distributions was that some photosynthetic species 



thrive equally well in water extremely poor in phos- 

 phate and in richer waters. The upper levels of vast 

 areas of the middle North Pacific are practically de- 

 void of phosphate. The concentration of phosphate ion 

 is less than 10 mg/m^, i.e., less than 10 parts of phos- 

 phate per billion parts of water. In the case of many 

 species studied, this area of low nutrient content was 

 not in any measure a barrier to distribution. Thus, it 

 is apparent that these species of peridinians can utilize 

 extremely low concentrations of nutrient salts. This 

 phenomenon is undoubtedly correlated with the normal 

 seasonal appearance of peridinians following the diatom 

 outbursts of northern waters during the spring and fall. 



INTRODUCTION 



In 1928 the Department of Terrestrial Magnetism 

 of the Carnegie Institution of Washington sent out its 

 nonmagnetic ship Carnegie on a world cruise of all the 

 major oceans exclusive of the Arctic. In addition to the 

 investigations of earth magnetism there was conducted 

 a program of oceanographic investigations. This pro- 

 gram included the collection of plankton samples and the 

 determination of hydrographic conditions at regular in- 

 tervals. Unfortunately, the cruise was brought to an 

 untimely end by the destruction of the vessel before it 

 had visited the Indian and Antarctic oceans. However, 

 162 stations were occupied over extensive areas of the 

 Pacific and North Atlantic oceans. In 1929 the author 

 was placed in charge of the biological work on board, 

 and at the termination of the cruise he was given charge 

 of the biological collections. 



The extensive nature of the collections permitted, 

 not only a detailed taxonomic analysis, but also a study 

 of geographic distribution based on comparable materi- 

 al. The simultaneous collecting of biological samples 

 and hydrographic data also offered a rare opportimity to 

 study the relations between the pelagic organisms and 

 their environmental conditions. 



After certain general quantitative studies of the 

 plankton were made, a study was begun which would lead 

 to a general knowledge of the plankton commimities in 

 the various regions and to a knowledge of the relation of 

 the individual planktons to each other and to environmen- 

 tal conditions. As a foundation for this it was necessary 

 first to compile lists of the species occurring at each 

 station. 



As a preliminary to this program the organisms in 

 the samples were sorted according to groups and each 

 group was submitted to a systematist for identification 

 and analysis. The author selected the Peridineae (Dino- 

 flagellata) for his own special study. 



These introductory remarks have been made in or- 

 der to give some idea of the origin of the material and 

 of the general scientific inquiry of which this report 

 forms a part. The discussion that follows is restricted 

 entirely to the peridinians. 



It was originally planned to make a comprehensive 

 study of this group in the Carnegie collection mainly 

 from the standpoint of geographic distribution and ecol- 

 ogy. A florlstlc treatment, naturally, would be the foun- 



dation for such a study. The analysis, however, was not 

 far advanced before it was realized that no thorough and 

 certain floristic treatment of the Peridineae was possi- 

 ble in the present state of the taxonomy of the group. It 

 was found that not a single genus of the group was cov- 

 ered by an exhaustive monograph which would enable 

 one to make identifications of the species with any de- 

 gree of certainty. As a consequence, the floristic anal- 

 ysis had to be preceded by a thoroughgoing taxonomic 

 study. 



The present paper deals with a small part of the 

 peridinian problem of the Carnegie material. It pertains 

 to certain forms of the order Peridiniales which were 

 selected for study and subjected to a careful morpholog- 

 ical analysis with the three following objects in mind: 

 (1) to establish a standard for the analysis and the re- 

 cording of the morphology of peridinian species; (2) to 

 acquire a knowledge of the detailed skeletal morphology 

 of some of the species; (3) to study variation within the 

 group by subjecting a few forms to intensive analysis; 

 and (4) to contribute to the concepts of the relationships 

 of the genera of the Peridiniales. 



The Carnegie material afforded interesting compar- 

 ative material because it contained not only rare tropi- 

 cal forms, but also temperate and subpolar material 

 from widely separated regions. 



Assistance in the routine census of the samples and 

 In the preparation of preliminary camera lucida sketch- 

 es was given by Mrs. N. Bronikovsky. Most of the fin- 

 ished ink drawings and wash drawings were executed by 

 Mr. Charles A. Dawson. The investigations were car- 

 ried out at the Hopkins Marine Station, Pacific Grove, 

 California through the courtesy of Dr. W. K. Fisher, Di- 

 rector. Valuable critical advice was received through- 

 out the Investigations from Dr. Tage Skogsberg, under 

 whose direction the work progressed. The pursuance of 

 the investigations was made possible through the good 

 offices of Dr. J. A. Fleming, Director of the Department 

 of Terrestrial Magnetism of the Carnegie Institution of 

 Washington, who has been in charge of the oceanograph- 

 ic program of the Carnegie and who has lent his contin- 

 uous interest and support to the biological work. To all 

 these I wish to express my deep appreciation for their 

 sympathetic assistance in the furtherance of the work. 



