228 MEMOIRS OF THE UNIVERSITY OF CALIFORNIA 



right side is somewhat more convex than the left. It has a length on the left and right sides of 

 0.36 and 0.43 respectively of the total length of the body. The hypocone is constricted slightly 

 a short distance beyond the girdle, expands in the posterior third and is rounded posteriorly, 

 with broad, hemispherical antapex. In the region of the girdle it flares out to form a broad lip. 



The girdle is premedian, its proximal junction with the sulcus occurring at a distance from 

 the apex of 0.36 of the total length of the body. It turns posteriorly, at an angle of 25° with 

 the transverse plane of the body, for a short distance, then passes almost transversely around 

 the body with a slight anterior deflection. Its distal end makes a short, abrupt posterior turn, 

 meeting the sulcus at an angle of 40° from the transverse plane of the body. The furrow is 

 wide, about 0.05 trausdiameter, and deeply impressed, its anterior lip undercut and its posterior 

 one gradually rounded. Both borders are raised considerably above the surrounding surface 

 of the body. The sulcus extends from the apex to the antapex in a slightly sinuous line. The 

 trough is shallow and narrow with a slight widening at the junctions with the girdle, and fading 

 out near both apices. The anterior flagellar pore opens at the proximal junction of girdle and 

 sulcus, the posterior pore at the distal junction. 



The nucleus is ellipsoidal and is found in the anterior part of the body. It is filled with 

 coarse chromatin strands. Its major and minor axes are about 0.32 and 0.27 trausdiameter in 

 length respectively. 



The protoplasm is finely granular, grey green in color, and contains many large, pinkish 

 vacuoles. Distinct alveoli are sometimes found in the peripheral zone (fig. Z, 11). The centro- 

 posterior part of the body is filled with a large, irregular body, pale pink in color, containing 

 a smaller yellow-green body near its center. This indicates a holozoic type of nutrition. Pusules 

 were not in evidence in the individual studied. 



A distinct pellicle is present of slightly greater consistency than most of these organisms 

 possess. Tliis is shown in the fact that it is occasionally found in preserved material with body 

 intact, the only recognizable Gymnodinium we have met in our examination of several hundred 

 plankton catches made at La Jolla and preserved in formalin. The surface is covered with longi- 

 tudinal, equidistant ribs, yellow green in color, which are raised slightly above the surface near 

 the middle of the body, gradually sinking and continuing as surface lines to the apices. It may 

 also present high ridges on the surface. The girdle is outlined with lines of the same yellow- 

 green color. 



Dimensions. — Length, 103/'- ; transdiameter, 70/^ ; axes of nucleus, 23/^ and 19m. 



OccuERENCE. — One individual was taken June 12, 1917, from a surface haul 

 at the end of the pier at tlie Biological Station at La Jolla, California. It was 

 also found in material preserved in formalin that had been collected September 

 24, 1904. 10 miles off La Jolla, in a surface haul with a No. 20 silk net. 



Comparisons. — Although showing no differentiated ectoplasm of quite the 

 same t^'pe as G. dogicli and G. pachiidcmmtum (figs. AA, 1, 5), yet its thickened 

 perijilast places it in the same group with them. In the presence of distinct 

 ribs on the surface, as distinguished from striae or furrows, it stands almost 

 alone in GymnodiniuH) , G. sulcatum alone showing a few ridges on the hypocone. 

 Amphidinium fastigiurn exhibits the same type of surface markings, though the 

 ridsjes are fewer in number. 



