14 



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



Tabulata, in which the second anterior intercalary 

 borders the third and fourth or the fourth and fifth pre- 

 cingular plates (fig. 5C). 



Conica . in which the second anterior intercalary 

 touches the third, fourth, and fifth precingulars (fig. 5B). 



Oceanica . in which the second intercalary touches 

 only the fourth precingular (fig. 5A). 



Metaperidinium was divided into four sections, as 

 follows: 



Pyriformia , in which the second anterior intercalary 

 plate touches two precingular plates, as in section Ta - 

 bulata of Orthoperidinium (fig. 5C). 



Paraperidinium , in which the second intercalary bor- 

 ders the third, fourth, and fifth precingulars (fig. 5B); 

 the first apical plate is bounded by six of the major 

 plates of the epitheca (fig. 4C): the second apical and 

 first and second precingulars on the left side, the fourth 

 apical and sixth and seventh precingulars on the right 

 side. Jorgensen did not give this group subgeneric rank 

 because there was considerable variation in the length 

 of the suture between the first apical and sixth precin- 

 gular plates; the suture is sometimes quite short. 



Humilia . in which the second intercalary touches only 

 the fourth precingular (fig. 5A); with solid antapical 

 horns. 

 Divergens , as Humilia but with hollow antapical horns. 



Jorgensen thus established not less than seven cat- 

 egories for the grouping of the species of Peridinium . 

 The number had thus become greater than when Gran 

 devised his simple classification, and it demanded a 

 more rigorous examination of the material. 



Although the thecal plates in Peridinium were 

 known by Jorgensen to present several patterns, the 

 number of plates in the theca was considered by him to 

 be constant. He (1913) described the genus as having 

 three anterior intercalary plates. Forms which had 

 only two intercalaries and which had been included in 

 Peridinium by others he placed in a new genus, Archae- 

 peridinium (fig. 6B). 



Jorgensen's comprehensive classification of the Pe- 

 ridinium species on the basis of the plate pattern laid 

 the foundation for a clearer understanding of the com- 

 position of, and the relationships within, the genus than 

 had ever before been possible. It promised to end the 

 taxonomic difficulties which this genus presented. His 

 classification was accepted by practically all later 

 workers up to the present time and has been extremely 

 helpful. 



As is shown in this paper, however, even this sys- 

 tem is not adequate for the proper classification of the 

 great number of variants which occur. 



Paulsen (1931) revised the system of Jorgensen 

 (see also Peters, 1928, and Dangeard, 1927). He con- 

 sidered the classification of Jorgensen unnatural, and 

 proposed a system in which not only the plate pattern, . 

 but a combination of plate pattern and other characters 

 was used. He abolished the subgenera of Jorgensen but 

 retained the sections with some revision. 



Paulsen (1931) referred to JOrgensen's Archaeperi - 

 dinium as a subgenus of Peridinium , as had been done 

 by Lebour (1925) and others. This subgenus is charac- 

 terized by having only two anterior intercalary plates. 



The second subgenus, with three intercalary plates, 

 Paulsen called Veroperidinium . This is equivalent to 

 the subgenus Peridinium proper of Leboiir. 



Paulsen divided the subgenus Archaeperidinium into 

 two sections: 



Avellana , in which the two intercalaries are equal. 



Excentrica , in which the two intercalaries are very un- 

 equal. 



The subgenus Veroperidinium he divided into eight 

 sections, seven of which corresponded roughly to the 

 sections of JOrgensen. The eighth section, Paradiver - 

 gentia, was new. A summary of his sections of Vero - 

 peridinium follows. In describing the relation of the 

 dorsal plates he used the terms "quadra," "penta,"and 

 "hexa" to designate the number of sides on the second 

 anterior intercalary, and "ortho," "meta," and "para" 

 to designate a four, five, or six-sided first apical. 



Pellucida : Para hexa, rarely para penta or quadra or 

 meta hexa. Right-handed. Without antapical horns; has 

 two, or more frequently three, antapical spines. This 

 section corresponds to Paraperidinium of Jorgensen. 



Humilia : Meta quadra. Right-handed, without horns, 

 but often with two antapical spines. 



P yriformia : Meta penta, rarely quadra or hexa. Right- 

 handed, without antapical horns, but in general has two 

 antapical spines. 



Tabulata : Ortho penta or hexa or quadra. Left-handed 

 or with circular girdle. Cell round, without horns or 

 spines, or with slight spines. 



Paradivergentia : Para quadra or hexa. Right-handed 

 or with circular girdle; with two hollow antapical horns. 



Divergentia (=Divergens Jorgensen): Meta quadra, 

 rarely penta. Girdle circular or right-handed; with two 

 hollow antapical horns. 



Oceanica : Ortho quadra, rarely penta or hexa (or even 

 para). Left-handed. Girdle oblique relative to the lon- 

 gitudinal axis of the body. Epitheca narrows into an ap- 

 ical horn; two hollow antapical horns. 



Conica: Ortho hexa, more rarely penta or quadra. 

 Girdle circular or left-handed. Body square or rhom- 

 boid in ventral view, without apical horn but usually 

 with two hollow antapical horns. 



Paulsen's classification is an improvement over 

 Jorgensen's (1913), for it takes into consideration the 

 occurrence of a greater number of combinations of char- 

 acters. In so doing, however, Paulsen acknowledged the 

 occurrence of a greater number of variations in the 

 characters which have been used as fundamental taxo- 

 nomic units. 



All the classifications devised so far have been 

 based on a certain stability of the plate pattei-n within 

 the species, particularly in the region of the first apical 

 plate and the dorsal epithecal plates. Furthermore, all 

 are based on the presence of three anterior intercalary 

 plates in Peridinium proper. As is shown below, in the 

 present investigations, forms in the section Oceanica 

 have been found with only two intercalary plates. 



It should finally be noted that should a subgeneric 

 classification be re-established for the sections, this 

 must be done with due consideration to the international 

 rules of nomenclature. When a new classification is 

 proposed, there is no justification for the introduction 

 of completely new terms. Old names must be retained, 

 with only the termination changing if they are given al- 

 tered rank (International Rules of Botanical Nomencla- 

 ture, 1935, art. 51). These rules were completely disre- 

 garded by JOrgensen and Paulsen. Thus Gran's subgenus 

 Protoperidinlum. for Instance, has not been perpetuated. 



