KOFOID AND SWEZY: UNARMORED DINOFLAGELLATA 85 



but with complication in life history resulting from the parasitic habit, in the 

 Blastodiniidae. 



We have withdrawn XocfilKni from the G,ystoflagellidae and placed it as 

 one of the Gpnnodinioidae, diverging at a low level in the specialization of the 

 group. The "Pyrocystaceae" of ]\Iurray, Apstein, and West disappear wholly 

 as merely a phase of the life history of other, and in some cases as yet unknown, 

 dinoflagellates. 



Development within the Group. — Within the diuoflagellate group as a 

 whole several distinct lines of morphological development with resulting speci- 

 ation may be traced. One of these lines follows the differentiation of the struc- 

 tures correlated with the motor organelles. These structures, the girdle and 

 sulcus, form the most characteristic features of the dinoflagellates and are the 

 ones having the greatest value for diagnostic purposes. 



The first beginnings of the girdle and sulcus in the genus Protodinifer and 

 their continued development in OxijrrMs (figs. R, 2, 3) have ah-eady been noted. 

 It is, however, within the family Gymnodiniidae that they reach their typical 

 form and also their greatest development in the Dinotlagellata, together with 

 the torsion of the body which is closely dependent thereon. In this group the 

 line of increasing specialization presents an orthogenetic series notable for its 

 well defined, progressive differentiation that links tlie members of the family 

 closely together. Ilcmiflitiiiim, while probably not the most primitive genus in 

 the family, yet stands near the base of development of these two critical features 

 of the Dinoflagellata. In this genus the girdle is short, its length being 0.5 turn 

 around the body, with the slilcus extending from the girdle to the antapex (fig. 

 C, 1), and with both flagella arising near or at the same midventral point. The 

 development of these structures in Hemkliuium marks a distinct advance be- 

 yond that attained by the genus 0.rtjrrhis (fig. K, 3) in that the girdle and 

 sulcus have definitely marked borders, sharply delimiting them. 



In the genus Amphidiiiium (fig. C, 2, 3) the girdle has lengthened to a 

 complete turn around the body, its position being anterior, instead of median, 

 as in Hewidiiiiutii, thus increasing the length of the sulcus and hypoeone and 

 decreasing that of the epicone. In maiw of the species of this genus, like 

 Hemidinium, Oxyrrhin, and earlier forms, the flagella arise near together at 

 the proximal end of the girdle (fig. R). In a few species of Ampliidinmm, 

 however, the flagella have become more or less widely separated (figs. U, 1, 4, 6). 

 In the further development of these forms this becomes the usual condition, 

 as in Gyrodinium (figs. CC, DD) and Cochlodinium (figs. GG, HH). The 

 sulcus also may increase in length, extending from the apex to the antapex. 



In Gynmodinium we find a type of girdle similar to that of Amphidinium, 

 l)ut in this genus its location has become sul)median. or at least has moved 

 considerably posterior to its ])osition in AiiiidtUliiiiani, with a resulting increase 

 in the relative size of the epicone (figs. C, 4, 5), G. doma (fig. C, 4) represents 

 a stage of this posterior migration which is only slightly removed from the 

 condition found in Aniphidinium scissu))i (fig. C, 3). In Gymnodinium the 



