STUDIES IN THE MORPHOLOGY, TAXONOMY, AND ECOLOGY OF THE PERIDINIALES 



ristic treatments of some group or groups of the Peri- 

 dineae; the remaining 300 deal with cytological, ecolog- 

 ical, and physiological problems. Of the systematic 

 papers, less than 5 per cent present critical analytical 

 treatments of the species from either the taxonomic or 

 the morphologic viewpoint. 



Forms Treated in this Report 



Of the fourteen families in the order Peridiniales, 

 this report deals with representatives of five. A mono- 

 graphic treatment has been given of the monogeneric 

 family Ceratocoryaceae. This was due to the fact that 

 ample material was available for making a complete 

 skeletal analysis of every known species. Whereas in 

 Ceratocoryaceae species are not difficult to define, in 

 the family Peridiniaceae the species seem to be in an 

 \instable condition; extreme variability frequently 

 makes a delimitation of species a difficult task, indeed. 

 One genus in this family was selected for study, viz., 

 Peridinium . Of its two hundred or more species, those 

 related to Peridinium depressum Bailey were selected 

 for intensive studies of the variation in body shape and 

 plate pattern. Representatives from other parts of this 

 large genus were also analyzed, viz., P. crassipes Ko- 

 foid, P. truncatum n.sp., and P. pallidum Ostenfeld. In 

 an attempt to probe further into the interfamily rela- 

 tionships, work was also done on three other families: 

 Ceratiaceae, Goniodomaceae, and Gonyaulacaceae. One 

 species from each of the first two was investigated, viz., 

 Ceratium p avillardii Jorgensen and Goniodoma polyedri - 

 cum Pouchet; and from the family Gonyaulacaceae four 

 species were analyzed: Gonyauiax pacifica Kofoid, Gon- 

 yaulax fusiformis n.sp., Acanthogonyaulax spinifera 

 (Murray and Whitting) Graham, and Spiraulax kofoidii 

 new name. 



Of the twenty-nine forms treated in this paper, 

 there are six new species, three new varieties, and six 



new forms. Two old specific names have been replaced. 



Following is a complete list of the forms included 

 in this report: 



Family Goniodomaceae 

 Goniodoma polyedricum Pouchet 



Family Ceratocoryaceae 

 Ceratocorys horrida Stein 

 C. armata (Schutt) Kofoid 

 C. reticulata n.sp. 

 C. aultii n. sp. 

 C. bipes (Cleve) Kofoid 

 C. skogsbergii n. sp. 

 C. gouretii Paulsen 



Family Gonyaulacaceae 

 Gonyauiax pacifica Kofoid 

 G. fusiformis n.sp. 

 Acanthogonyaulax spinifera (Murray and Whitting) 



Graham 

 Spiraulax kofoidii new name 



Family Peridiniaceae 

 Peridinium depressum Bailey 

 P. depressum var. parallelum Broch 

 P. depressum var. rectius n. var. 

 P. depressum var. convexius n. var. 

 P. depressum f. bisintercalares n.f. 

 P. depressum f. multitabulatum n.f. 

 P. claudicanoides n.sp. 

 P. oceanicum Vanhoffen 

 P. oceanicum var. tenellum n.var. 

 P. oceanicum f. spiniferum n.f. 

 P. oceanicum f. bisintercalares. n.f. 

 P. oceanicum f. tricornutum n.f. 

 P. crassipes Kofoid 

 P. truncatum n.sp. 

 P. truncatum f. acutum n.f. 

 P. pallidum Ostenfeld 



Family Ceratiaceae 

 Ceratium pavillardii Jorgensen 



RELATIONSHIPS AMONG THE GENERA 



General Considerations 



Our ideas of the relationships of the genera must at 

 present be based on the degree of similarity in the skel- 

 etal structures, since the cytology of the order is alto- 

 gether too little known to be used for this purpose. For- 

 tunately, the skeletons of these forms are complex and 

 hence present a multitude of morphological characters 

 useful in taxonomic studies. These characters have not 

 been the basis for any satisfactory discussion of inter- 

 generic relationships; indeed, so far no one has ventured 

 Into such a discussion. Ideas concerning these relation- 

 ships have been expressed only by the grouping of the 

 genera into families, without any discussion of the justi- 

 fication for doing so (see, however, Lebour, 1922, on the 

 origin of Peridinium ). 



The absence of such evolutionary studies is proba- 

 bly due to the apparent lack of order in the great varie- 

 ty of plate patterns which are presented by the various 

 genera. It is extremely difficult to select, from this 

 kaleidoscopic array of patterns, characters which are of 

 fundamental generic or family Importance. As stressed 



above, however, the incompleteness and undoubted inac- 

 curacies in our knowledge of the skeletal features have 

 greatly aggravated this situation. Doubtless the situation 

 in nature is not so chaotic as present knowledge indicates. 



The skeletal features which are the most fundamen- 

 tal from the standpoint of taxonomy are the number and 

 arrangement of the thecal plates. The body shape, the 

 lists and spines, and other such characters are of sec- 

 ondary importance. 



In regard to the number of plates, there are variouf 

 ways in which evolution may have taken place. For in- 

 stance, primitive forms may have had relatively few 

 plates and evolution may have progressed by the split- 

 ting of plates or by the insertion of newly formed plates; 

 or the primitive forms may have had a large number of 

 plates and evolution may have proceeded by the fusion 

 and loss of plates; or the processes of Increase and de- 

 crease may have taken place simultaneously in different 

 parts of the body. 



Whatever has been the progress of evolution, it has 

 not been uniform or parallel in all parts of the theca. 

 Today there are some genera with the same number of 



