KOFOID AND SWEZY: UNARMORED DINOFLAGELLATA 123 



Diagnosis. — Body asymmetrically ellipsoidal, flattened on three sides, rotund 

 on the left; its length 1.75 transdiameters; girdle a descending left spiral of 

 0.5 turn, its anterior lip protuberant; sulcus reaching postmargin; chromato- 

 phores yellow to brown. Length, 24-28/^. Fresh- water ponds and pools in clear 

 water. Europe. 



Description. — The body is noticeably asymmetrically ellipsoidal with flattened ventral, right, 

 and dorsal faces, but rotund left face interrupted by the protuberant anterior lip of the girdle. 

 Its length is 1.5 to 1.65 transdiameters at the widest part, which is at the base of the epicone. The 

 epicone and hypocone are subequal, botli with asymmetrical, subhemispheroidal apices, the antapex 

 sometimes exhibiting a shallow suleal notch. 



The girdle is incomplete, making 0.5 turn of an evenly descending left spiral with a total 

 displacement of 0.33 of the length of the body. Its anterior lip on the left margin is strongly 

 protuberant, hence the specific name. The posterior lip is more rounded than the anterior. It 

 fades out distally at the middorsal line. The sulcus is confined to the h.ypocone and extends as 

 a straight furrow from the girdle to tlie postmargin in which it may form a shallow notch. The 

 two flagella originate near tlie junction of girdle and sulcus in close proximity. 



The nucleus is a small ellipsoid in the left posterior part of the hypocone. Its axes are 0.30 

 and 0.25 transdiameter in length respectively. Its membrane appears to be double-contoured, and 

 typical chromatin threads have not, as yet, been figured in it. 



The peripheral cytoplasm is filled with elliptical reddish brown chromatophores and reddish 

 brown oil drops as stated by Schilling (1913) to be present in the spherical cyst. Klebs 

 (1883) states that this species has a distinct, separable cell wall which swells in soda and sulphuric 

 acid, stains yellow in iodine and brown in chloride of zinc. Schilling (1913) states that it is 

 composed of cellulose, though Klebs had distinctly noted that it does not stain blue on test for 

 cellulose. Further investigation is needed to determine the presence of this so-called cell wall 

 and to determine its nature as eomiDared with the pellicle of the Gymuodiuioidae with which we 

 here include it. 



Dimensions. — Length, 24-28/s transdiameter, 16-17^; nucleus, 7-8/^; cyst, 

 20m. 



Occurrence. — Originally described by Stein (1883) from Prague, Austria, 

 and later reported by Klebs (1883), Schilling (1891, 1913), Levander (1894, 

 1900rt, 1901), France (1893), and Dalle Torre (1885), from continental fresh 

 waters in Europe from the Tyrol to Finland. Schilling (1913) states that it 

 is rather common in shaded fresh-water pools, ponds, ditches and swamps in 

 clear water. Butsdiinsky (1897) reports it as rare in a salt lake near Odessa, 

 Russia, with a concentration of 5 per cent. Since he also reports O.rijrrhi's 

 morinum (as GhjpMdium niarinmn) from the same water, it seems improbable 

 that he has confused the two species. There is no other record of the species 

 from salt or brackish water. Its occurrence therein requires verification. It 

 has not been reported from the Americas. 



Comparisons. — It appears to l)e quite distinct from //. ochraceum of Lev- 

 ander (1900a), who found them both in temporary rain-water pools on rocks 

 in Finland. Both have the thin pellicle, but differ in the position of the girdle, 

 which in this species is more nearh^ equatorial, as in Gymnodinium, while in 

 G. ochraceum it is anterior, as in Amphidinium. 



