8 MEMOIRS OF THE UNIVERSITY OF CALIFORNIA 



For the eouvenienee of the reader the following l^rief outline of the Dino- 

 flagellata is here given. The gronp contains t\YO orders, the Adiniferidea with- 

 out a girdle and the Diniferidea with a girdle. The former contains two tribes, 

 the Athecatoidae, without cuii'ass, as naplodiniuni, and the Thecatoidae, with 

 enveloping cnirass, as Prorocentrnm. The Diniferidea are likewise divided 

 into two groups, the G^annodinioidae or naked forms and the Peridinioidae or 

 armored forms, such as Peridinmm. Both of these groups contain a few species 

 of doubtful relationships. The Grvmnodinioidae contains seven families, to wit, 

 Protodiniferidae, Gymnodiniidae, Polj^krikidae, Noctilucidae, Pouchetiidae, 

 Blastodiniidae, and Cystodiniidae. 



In the following discussion of the tribe Gpnnodinioidae the chief emphasis 

 is laid ixpon those members of the groujD comprised in the families Protodini- 

 feridae. G^annodiniidae, Pouchetiidae and the genus PaviUardia in the Nocti- 

 hicidae. Attention is not confined, however, to these forms alone, but ilhistrative 

 material is drawn upon from the entire Dinoflagellata where pertinent to the 

 subject in hand. 



Size and Forim. — As a group the Flagellata probably has a smaller average 

 size for its members than most of the other large groups of Protozoa. The 

 two subdivisions of this group which attain the maximum size found within it 

 are the Trichonyniphidae and the Dinoflagellata, and of these two the latter 

 presents some of the greatest variations in size found within the group, having, 

 at one end of the scale, the largest individuals and, at the other end, some of 

 the smaller, though not the smallest ones, thus far described for the Flagellata. 



Within the Gjannodiuioidae (excepting A^octilMca) these variations in size 

 extend from 11/* to 212/* for the motile flagellated individuals, but some of the 

 parasitic forms attain a lengih of 700/*. The maxinumi size within the group 

 is, however, attained by NoctHuca, which may have a transdiameter of 1 to 

 1.5 mm. The average length for members of the G^^nnodiniidae is about 100/*. 

 The greatest size in this family is found in the more specialized members of 

 Gymnodinmm., such as G. pachydermatum and G. dogieli (figs. AA, 5, 8), and 

 in Gochlodinmni, such as C. strangulatum (fig. GG, 8). Next to these in size 

 comes the Pouchetiidae, whose largest members are somewhat smaller than the 

 largest meml^ers of the other group, Init whose smallest members do not reach 

 the lower extreme in size (figs. KK-RR), all the species being nearer the 

 average than are the species in the other genera, Gymnodinium, Gyrodinium, 

 and Oochlodinium. 



The variations in size within the species cannot be stated with any degree 

 of certainty, owing to the lack of knowledge of the amount of growth that may 

 take place within a single developmental cycle, and often also to the small 

 number of individuals of a single species that can be found, even with pro- 

 longed searching. In forms which are obvioiisly members of a single species, 

 variations of a third, or slightly more, may sometunes be noted in the length. 



Other factors which make a determination of the variation in size within 

 the species very difficult are the extreme sensitiveness and ready response of 



