KOPOID AND SWEZY: UNARMORED DINOPLAGELLATA 121 



Key to the Geneba of the Family Gymnodiniidae 



1. Girdle of 0.5 turn only Hemidinium Stein 



2. Girdle anterior, epicone relatively minute Amphidinium Clap, and Lach. 



3. Girdle submedian, displaced less than 0.2 total length of body Gymnodinium Stein 



4. Girdle posterior, without displacement, sulcus with long apical loop Torodinium gen. nov. 



5. Girdle displaced 0.2 or more of total length of bo<ly with torsion of 1 to less than 1 .5 turns.... 



Gyrodinium nom. sp. nov. 



6. Girdle with torsion of 1.5 or more turns Cochlodinium Schiitt 



HEMIDINIUM Stein 



Text figure R, 4 



Hemidinium Stein (1888), pp. 91, 97, pi. 2, figs. 23-26. 



Hemidinium, Eyferth (1879), p. 19. 



Hemidinium, Saville-Keut (1880-82^, pp. 210, 440, 442. 



Hemidinium, Bergh (1882), p. G94; (1884), pp. 385, 387. 



Hemidinium, Biitscbli (1885), pp. 1008, 1016, pi. 51, fig. 3. 



Hemddinium, Delage and Herouard (1896), p. 384, fig. 667. 



Hemidinium, Schiitt (1896), p. 4, fig. 3. 



Hemidinium, Mez (1898), p. 217, pi. 6, fig. 286. 



Hemidinium, Schilling (1891ff.), PP- 274, 275, pi. 8, figs. 23-25, pi. 10, fig. 8. 



Hemidinium, Lemraerraann (1900), p. 115; (1901), p. 358; (1902), p. 260; (1910), pp. 



580, 617, 618, figs. 14-18. 

 Hemidinium, Sehoniehen and Kalberlah (1900), p. 230, pi. 8, fig. 1 ; (1909), p. 251, pi. 8, 



fig.l. 

 Hemidinium, Willey anl Hiekson (1901), p. 184, fig. 10. 

 Hemidinium, Paulsen (1908), pp. 94, 95, fig. 127. 

 Hemidinium, Conn (1905), p. 39. 

 Hemddinium, Cavers (1913), p. 183, fig. 9. 



Diagnosis. — Gjannodiniidac with incomj)lete girdle of 0.5 turn; 2 species, 

 from fresh water. 



Description. — The body is asymmetrically ellipsoidal to ellipsoidal in form; girdle median 

 to premedian, incomplete, forming less than 0.5 turn of a dcscentliug left spiral; sulcus confined 

 to the hypocone. The nucleus is ellipsoidal to spheroidal with chromatin granules. The chro- 

 matophores are yellowish to brownish. No stigma. Small species, 24-33^ long. Presh water, 

 Europe. Two species. 



Historical Discussion. — This genus was described by Stein (1883) and 

 included but a single species, H. nasutum Stein, the type species of the genus. 

 It has no other characteristics of a primitive nature except holophytic nutri- 

 tion. Levander later (1900r/) added a second species to the genus, H. ochraceum, 

 also from fresh Avater. 



