SUMMARY 



1. This monograpli includes all known unarmored and free-living Dinofla- 

 gellata. It is based on a study of the marine forms of the San Diego region 

 made at the Marine Biological Station of the Seripps Institution for Biological 

 Research. It includes 223 species belonging to 16 genera. 



2. The following genera are new: Protodinifer, Gyrodinium, Turodinmni, 

 Pavillardia, Protopsis, Nematodimum, and P voter ijtliopsis. 



3. One hundred and seventeen species are new, distributed as follows in the 

 genera: Protodinifer, 1; Am pMdinium , 12; Gi/mnodiniuni, 36; Gyrodiniimi, 

 23; CocJdodiuiioii, 21; Torodinium, 1; PavilJardia, 1; Protopsis, 1; Neinafo-^ 

 dinium, 2 ; Ponchetia, 12; Proferi/fliropsis, 1 ; ErijtJiropsis, 6; a total of 117 new 

 species. 



4. The Dinoflagellata have evolved from a primitive, biflagellated flagellate, 

 by differentiation of the two primitive, similar, anterior flagella. One becomes 

 rilibon-like, with short undidations, and is the transverse flagellmn of the Dini- 

 feridia. The other flagellum becomes the longitudinal trailing flagellum by the 

 posterior migration of the flagellar pore to the midventral region. In the 

 Adiniferidea the flagella are differentiated but the pore has not migrated 

 posteriorly. 



5. The unarmored forms are more primitive than the armored ones, the 

 Athecatoidae than the Thecatoidae in the Adiniferidea, the Gjaimodinioidae 

 than the Peridinioidae in the Diniferidea. 



6. The new genus Protodinifer is a primitive form with anterior, differen- 

 tiated flagella, and partial girdle feeldy developed. It sIioavs affinities to the 

 Adiniferidea and suggests the origin of botli Adiniferidea and Diniferidea from 

 unarmored, ancestral forms allied to it. 



7. The two flagella, transverse and longitudinal, with the two channels in 

 tlie surface of the body in which they lie, the girdle and sulcus, are superficial 

 organs in active contact with the environment, and are extensively modified in 

 an orthogenetic manner in the evolution of the genera, and in speciation within 

 the genera. 



8. The modifications consist of a progressive elongation of the girdle, with 

 accomxjanying torsion of the body in a left spiral up to four tui-ns. There is 

 also a ])rogressive torsion of the sulcus and its prolongation to tlie apex and 

 antapex, culminating in the genus Cochlodinimn. 



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