1911] Kofoid: The Genus Gonyaulax. 255 



acters such as surface markings, and outgrowths such as spines, 

 lists, and fins. 



The types of hodily form may all be traced back to modifica- 

 tions of a sphere, a type realized almost perfectly in G. sphae- 

 roidea and G. palustris, less so in G. scrippsae and G. turhynei. 

 This sphericity is retained in the posterior part of the body, in 

 the more conservative hypotheca in G. apiculata, G. fragilis, G. 

 digitale, G. scrippsae, G. diegensis, G. triacantha, and G. hyalina. 



Elongation of the body is apparent in the whole body in 6^. 

 apiculata and G. fragilis; in the apical region only in G. spinifera, 

 G. digitale, G. diegensis, and G. ceratocoroides, and especially in 

 G. mitra. Elongation of the epitheca as a whole is seen in the 

 large numbers of the polygramma group, G. polygramma, G. 

 kofoidi, and G. pacifica. Elongation of the hypotheca in excess 

 of that of the epitheca is noticeable in G. mitra, in G. milneri, and 

 G. ceratocoroides. Elongation with marked accompanying 

 attenuation of both halves is seen in the subgenus Fusigonyaulax 

 in its species hirostris, glyptorhynchus, and highleii. The polyhe- 

 dral form of bod.y is found in G. polyedra, G. milneri, and G. 

 ceratocoroides. In these the sutures are somewhat salient and 

 the plates flattened rather than convex. 



The most fundamental and characteristic structure in the 

 genus Gonyaulax, and for that matter in the Dinoflagellata, is 

 the girdle, the trough in which the ribbon-like protoplasmic 

 sheet called the transverse flagellum lies. Throughout all species 

 of Gonyaulax this girdle is wound in a descending spiral about 

 the body, the amount of descent varying from one to seven girdle 

 widths in different species. The amount of displacement is 

 characteristic for the species, subject however to some variation 

 within the species. An abrupt proximal curvature is distinctive 

 of some species, as for example of G. pacifica (pi. 15, fig. 35) 

 and G. triancantha (pi. 11, fig. 13) and a sweeping distal one of 

 G. diegensis (pi. 13, fig. 24). In G. spinifera (pi. 16, fig. 39) 

 and G. digitale (pi. 9, fig. 3) the girdle makes more than a com- 

 plete circuit of the body, the overhang of the two ends being 

 several girdle widths. 



The actual width of the girdle is fairly constant in all species. 



