200 University of California PubJicatio)ts i)i Zoology. [Vol.8 



thus far been observed by me. In the fission of thecate indi- 

 viduals the parental skeleton parts along uniformly definite 

 sutures as in Cerafium (see Kofoid, 1909a) in an irregular plane 

 at approximately right angles to the major axis of the spindle 

 of the dividing cell. This plane parts the antero-sinistral moiety 

 from the postero-dextral one. Chain formation occurs in con- 

 junction with thecal fission, in so far as my own observations and 

 the literature indicate, only in Gonyaulax catenata (Levander) 

 Kofoid, and in G. series, as I have elsewhere shown (1911c). 

 Chain formation of the plasma mass followed by .skeletal forma- 

 tion (le novo occurs in Gonyaulax series (see Kofoid, 1911a). 



The anterior moiety (see text-figures A-D and pi. 10, figs. 9, 

 10) receives from the ancestral skeleton all of the apical series, 

 and interior intercalaries when these are present, ])reeingulars 

 1" and 2", girdle plates ]-3, and posteingulars l"'—i"'. The pos- 

 terior moiety receives precingulars 3"-6", girdle plates 4-6, post- 

 eingulars 5"'-6"\ posterior intercalary 1>', and the antapical 1"" . 

 The fission line appears to pass through the tiagellai" pore and 

 the greater part, if not the whole, of the ventral area goes with 

 the posterior moiety. The path of the fission plane along the 

 sutures is clearly shown in text figures A-D. The precise loca- 

 tion of the fission line in the ventral area has not been accurately 

 determined as yet. The figure of Entz (1905, fig. 58) suggests 

 that this line passes through the fiagellar pore and separates the 

 anterior plate of the ventral area from the intermediates. Since 

 he does not distinguish the subdivisions of this area, or indeed 

 in his figures the other plates of the thecal wall, he has left the 

 matter still in some uncertainty. 



V. Subgenera and Species of Gonyaulax 



For convenience the species of Gonyaulax may be grouped 

 in three subgenera based upon the general form of the body. It 

 is somewhat difficult to define these groups in such a way as to 

 make the a,ssignment of every known species to one of the three 

 perfectly evident. A few aberrant species are in consequence 

 included in the larger subgenera. As a result of my examina- 

 tion of extensive material of this genus and of a critical review 



