298 MEMOIRS OF THE UNIVERSITY OF CALIFORNIA 



Gyrodinium dorsum sp. uov. 



Plate 1, figure 81 ; text figure CC, 19 



DiAGxosis. — A medium sized species with elongate ellipsoidal body, its length 

 1.83 transdiameters ; girdle postmedian, a descending left spiral, displaced 0.43 

 transdiameter ; color, Yello^Yish. Length, 72^. Pacific off La Jolla, California, 

 August. 



DESCRiPTioisr. — The body is elongate ellipsoidal with broad, rounded apices, nearly circular 

 in cross-section, its length 1.83 transdiameters at the widest part, which is at the girdle. The 

 epicone exceeds the hypocone in size, its length being greater by 0.31 of its own length. It is 

 elongate hemispherical in size with symmetrically roimded sides and broad apex. It has a length 

 on the left and right sides of 0.47 and 0.7 respectivelj' of the total length of the body. The 

 hypocone is hemispherical posteriorly with its sides very slightly elongate anteriorly and flaring 

 around the anterior margin. It has a length on the left and right sides of 0.4 and 0.25 respec- 

 tively of the total length of the body. 



The girdle is postmedian in position for the greater part of its length. Its proximal end joins 

 the sulcus at a distance from the apex of about 0.47 of the total length of the body. It sweeps 

 around the body in a descending left spiral with its distal end meeting the sulcus at a distance 

 from the apex of 0.7 of the total length of the body. The furrow has a width of 0.06 trans- 

 diameter, and is rather deeply impressed with smooth borders. The sulcus extends from near 

 the apex to near the antapex in a slightly sinuous course. The furrow is deep and varies some- 

 what in width throughout its course. The anterior flagellar pore opens at the anterior junction 

 of the girdle and sulcus, the posterior pore slightly posterior to the midpoint between the distal 

 junction and the antapex. 



The nucleus is spherical and is located in the posterior half of the body. It is densely filled 

 with chromatin threads. Its axis is about 0.66 transdiameter in length. 



A large sacklike pusule opens into each flagellar pore. The cj^toplasm is finely granidar. A 

 large food mass, olive buff in color, occupied a position above the nucleus. Scattered through 

 the peripheral layer of cytoplasm were numerous blue-green oil drops. The general color is 

 aniline yellow mixed with grey and shading into buckthoi-n brown at both apices. 



Dimensions. — Length, 72/^ ; transdiameter, 39/^ ; axis of nucleus, 25/*. 



OccrRRENCE. — A single individual was taken August 21, 1917, 5 miles off 

 La Jolla, California, in a haul from 83 meters to the surface and in a surface 

 temperature of 21-9 C. 



Synoxy:my. — Pouchet's form (1883), Gymnodinmm spiral c var. C, is prob- 

 ablv the same as our species. It is somewhat larger, 119/^ as compared Y-ith 

 72^1 in ours, but this is not too great for Yariations mthin the species. The 

 girdle is postmedian and its displacement is about the same as in Gyrodinium 

 dorsum. Its nucleus is spheroidal and in the plane of the posterior junction of 

 the girdle and sulcus. It differs greatly from G. spirale, both in the size and 

 shape of body and its lack of surface striae. 



Comparisons. — In only tY-o other species of Gyrodinium has the girdle 

 become posteriorly located, G. crassuni (fig. CC, 21), in Y'hich only a small 

 portion is anterior to the midjilane, and G. glaucum (fig. DD, 16), in which the 

 h\^ocone is a relatiYely small part of the body. 



