210 MEMOIRS OF THE UNIVERSITY OF CALIFORNIA 



Description. — The body is stout fusiform, conical anteriorly and rounded posteriorly, its 

 length 2.27 trarLsdiameters at the widest part. The girdle is placed far anteriorlj', dividing the 

 body into two veiy unequal portions. The hypoeone exceeds the epicone in length by 0.57 of 

 its own length. The epicone is conical (80°) with a blunt apex which is deflected slightly to 

 the dorsal side. The hj-pocone is roiuided at the antapex in ventral view, in lateral view is 

 asymmetrical, vrith dorsal side rounded and ventral flattened. On each side of tlie sulcus the 

 body is drawn out into a flap with the left one slightly wider than the right. 



The girdle forms a complete circle about the body at a distance from the apex of 0.29 of the 

 total length of the body. The furrow is narrow with a shallow trough. The sulcus begins at 

 the girdle and extends to the antapex. In the middle part of its course it is obscured by the 

 overlapping of the drawn-out borders, which become widely deflected posteriorly. 



The nucleus is an irregularly ellipsoidal body near the center of the hypoeone. Its major 

 and minor axes are about 0..57 and 0.40 transdiameters in length respectively. The body also 

 contained two large food masses (?) and numerous bright yellow, elliptical chromatophores, 

 those in the anterior lialf of the body being arranged in lines. 



Dimensions. — Length, 100/^ ; transdiameter, 44/^ ; axes of uucleus, 25a* and 19/*. 



Occurrence. — Figured by Lebour (1917&) from collections made in June 

 and July at Plymouth Sound, England. 



Synonymy. — Described by Lebour (1917&) as G. pseudonodUuca Pouchet, 

 it presents some dilfei-ences -s^diich separate it from that species, the most 

 striking ones being in the form of the girdle and the i^resenee of chromato- 

 phores. In Pouchet 's (1885fl) species the girdle turns posteriorly on the ven- 

 tral surface, the opposite ends meeting slightly posterior to the middle of the 

 body. In Lebour 's form it passes aromid the Ijody as a complete circle with 

 little posterior deflection. 



Comparisons. — Chromatophores are more frequently found in the fresh- 

 water species of Gymnodinium than in the marine forms. In this characteristic, 

 together with the relative size of epicone and the anterior position of the girdle, 

 it forms an intermediate species linking Gijmnodinium to A}Hpliidinium, but is 

 not otherwise more primitive than species previously treated here. It belongs 

 in the subgenus Gymnodinium. 



Gymnodinium fuscum (Ehrenberg) Stein 



Text figure X, 19 



Peridimum fuscum Ehrenberg (1834), pp. 270-271; (1835), pp. 126-127; (1838), p. 254, 

 pi. 22, fig. 15, date quoted on p. 254 as 1833 (1832) by Ehrenberg. 



P. fuscum, Dujardin (1841), p. 376. 



P. fuscum, Riess (1842), p. 35. 



P. fuscum, Perty (1852), p. 162. 



Heteraulacus fuscus, Diesing (1850), p. 100; (1866), as Hetcroaulax fusca, p. 95. 



Pcridinium fuscum, Bailey (1850), p. 46. 



P. fuscum, Claparede and Lachmann (1858-61), p. 406. 



P fuscum, Maggi (1874), p. 118; (1880), p. 9. 



P. fuscum. Stein (1878), pp. 2, 70, 72, 78, 88, 90. As Gijmuodiuium fuscum, (1878), pp. 

 95, 97; (1883), pi. 2, figs. 14-18. 



P. fuscus, Eyferth (1879), p. 19. 



