276 MEMOIRS OF THE UNIVERSITY OF CALIFORNIA 



is thus here a more or less steeply descending left spiral, usually nearer the 

 anterior than the posterior end, frequently occupying the middle third of the 

 body. In one species only, G. gJaucnm, is it located far posteriorly. The 

 amount of overlapping of the ends varies from none to about 0.5 transdiameter, 

 the latter amoimt being rare and foreshadowing the conditions in Cochlodinium 

 with its greater torsion of the l)ody. The greatest amount of overlapping or 

 overhanging is shown in G. contortion Schiitt (fig. CC, 22). 



The sulcus is variable in length, usually extending from or near the apex to 

 the antapex in a nearly straight line or with a varying amoimt of torsion, less 

 than 0.5 transdiameter. The sulcal region forms the area for the ingestion of 

 food, which will probably account for the variations in length and prominence 

 of its borders noted occasionally in indiAdduals of the same species. In one 

 species only, G. ochraccum (fig. DD, IT), it forms an antapical loop with a 

 torsion of 0.5 transdiameter below the distal junction of the sulcus and girdle, 

 resembling in this respect the more highly developed forms of Cochlodinium 

 and Pouchetia. A greatly developed apical loop is found in G. intortum sp. nov. 

 (fig. CC, 10), combined with an overhang of the girdle of 0.6 transdiameter 

 which more closely aligns it with Pouchetia than with other members of this 

 genus. Its lack of ocellus, however, excludes it from the genus Pouchetia. 



The chromatin contents of the nucleus of Gi/rodinium are always arranged 

 in moniliform threads. In two species, G. corallinnm sp. nov. and G. virgatum 

 sp. nov. (figs. DD, 12, 21), the nucleus is composed of two distinct regions, an 

 outer alveolar zone and an inner zone filled with chromatin granules, and separ- 

 ated by a distinct membrane. The nuclevis is usually located near the central 

 part of the body, rarely far anteriorly or posteriorly. 



The surface of Gfirodininm may be either smooth or striate, with a prepon- 

 derance of species showing a striate surface, differing in this respect from all 

 other genera in the G^annodiniidae. The striae may be continuous, unbroken 

 lines or may be composed of linear series of short da.shes. When pig-ment is 

 present in the body it is collected along the lines of striae and massed at the 

 ends of the lines, indicating a fundamental linear organization of the peripheral 

 c\i:oplasm (figs. DD, 9, 21). 



The color of the cytoijlasm in Gyrodinium is remarkable for its diversity 

 and brilliancy. It may be diffusely distributed as in G. truncus sp. nov. (pi. 3, 

 fig. 28), G. herhaceuni sp. nov. (pi. 10, fig. 109), and G. fissum sp. nov., confined 

 to chromatophores, as in G. mclo sp. nov. (pi. 5, fig. 50), G. foliaceum sp. nov., 

 G. fcdcatum sp. nov., and G. pnsillum (Schilling), or may take the form of pig- 

 ment, as in G. maculatum sp. nov. (pi. 6, fig. 62), G. corallinum sp. nov. (pi. 10, 

 fig. 117), G. ochraceum sp. nov. (pi. 7, fig. 76), G. virgatum sp. nov.. G. post- 

 macidatuyn sp. nov. (pi. 6, fig. 6-1). 



All the colors of the spectrmn are to be found within the species of this 

 genus, but most of them show some shades of yellow and green. G. macidatum 

 sjD. nov. (pi. 6, fig. 62), with its violet pigment, is the only species lying near 

 the violet end. G. hiconicum sp. nov. (pi. 4, fig. 46) and G. suljmarinum sp. nov. 



