KOFOID AND SWEZY: UNARMORED DINOFLAGELLATA 



87 



locomotion and sense organs, and with respect to the ocellus, of the Protozoa 

 as a whole. Prof apsis is clearly a generalized, primitive genus, with girdle and 

 sulcus still at the level of Gipnuodininm and Gtjrodinium, the ocellus scarcely 

 integrated and tlie coloration not advanced beyond the ochraceous stage preva- 

 lent in simpler G>annodinioidae. It is thus evident that this genus is most 

 closely related to the generalized species of Giimnndinium and Gi/rodiniion, 

 showing no advance beyond these forms, save in the development of its ocellus. 

 The presence of pigment in the more generalized species of Gyrodinium prob- 

 ably is related to the development of the pigmented portion of the ocellus or 

 melanosome in Pouchctia, Protopsis, and Erythropsis: 



Fig. T. Development of prod of Erythropsis. 1. Cochlodinium cavatum sp. nov. 2. Poucheita maeulata 

 sp. nov. 3. Proterythropsis crassicaudata sp. nov. 4. Erythropsis extrudens sp. nov. X 500. 



In the genus N'smatodinium (fig. NN) we have an offshoot of a group of 

 divergent species representing a considerable degree of specialization of the 

 girdle and sulcus. These are separated from the remainder of the family by 

 the presence of nematocysts. The only other genus of dinoflagellates with these 

 unique organs is the genus Polijkrikos. No apparent close relation exists be- 

 tween the two groups, however. This would suggest an independent origin for 

 these structures in Ncm(dodininm, unless, as may proljably be the case, the 

 connecting links between the two genera have disappeared. 



In the genus Pouclietia (figs. 00, PP) we find the extreme development of 

 the sulcus in length, torsion, extent of apical and antapical loops, and its con- 

 striction of the body. Here the girdle is usually shorter and less cons^ncuous 

 than the sulcus, unlike its condition in the lower genera where the sulcus is 

 still primitive, whereas the girdle may become more highly complicated as in 

 Cochlodinium. 



The close relationship of the family Gynmodiniidae and the family Pouche- 

 tiidae is clearly indicated in certain points in their structure. One line of 

 s])ecialization linking together these two grouj^s is found in the increasing 

 differentiation of the ventrosulcal region, culminating in the production of the 

 prod of Erythropsis. The l)eginnings of this line may be looked for in the 

 genus Coclilodinium. Here an increasing degree of mobility of the plastic 

 sulcal area near the posterior end of the body is present in C. convohdum (fig. 



