452 MEMOIRS OF THE UNIVERSITY OP CALIFORNIA 



The ocellus is quite large, 0.5 transdiameter in length, and is located just posterior to the 

 middle of the body, below the girdle, and apparently in the typical position at the left of the 

 intercingular sulcus. Its axis stands at about 45° above the horizontal and it is directed antero- 

 sinistrally. It is quite protuberant and appears to be crowded against the sulcus. It is of the 

 simple or concentrated type, consisting of a spherical lens and massive pyriform ( ?) melauosome. 

 The lens is somewhat irregularly subdivided into several unequal lamellae and is slightly 

 embedded on one face in the larger end of the melanosome, which is larger than the lens, its 

 major and minor axes being respectively 1.5 and 1.25 diameters of the lens in length. 



The color of the body is diffuse ochraceous. This species is often found in a transparent, 

 close fitting cyst within which binary fission occurs with resiilting temporary chain formation of 

 the two sister organisms. 



Dimensions. — Lengtli, 33m ; greatest transdiameter, 20m ; length of the ocellus, 

 10m. 



Occurrence. — Reported by Lohmann (1908, 1911) from the plankton of 

 the Baltic Sea at the entrance to Kiel Harbor from April to November, in 

 surface temperatures of 5° C to 19° C. The plankton was collected by the cen- 

 trifuge method and the numbers per 100 liters range from less than 500 or too 

 few for enumeration to 50,000. This maximmn was found on May 16, 1906, at 

 the surface in a temperature of 12?6 C, as shown in Lohmann 's table B. His 

 statement in the text (1908, p. 263) that the maxunum was 230,000 appears to 

 be in contradiction to the table and to his own previous citation of the 50,000 

 maximum. He finds the species avoiding the deeper waters at his collecting 

 station, where the depth was 15 to 16 meters. On the 23 days on which it was 

 found in the series of 60 sets of samples from different levels from April 12, 

 1905, to August 17, 1906, it occurred 15 times at the surface, 12 times at 5 meters, 

 and only 3 times at 15 meters. The inflttence of light is thus evident in its 

 distribution. 



Miss Lebour (1917&) reports it from Phnnouth Sound as "frequent in 

 simmier, especially in June." She states, however, that "this s]:)ecies is very 

 like Pouchet's figure (1885) of P. polijphemus var. nigra. The pigment, how- 

 ever, in his species is I'ed and this is always black." Since Pouehet did not 

 describe his Gymnodinium pohjpliemns var. nigrum until 1887, and never stated, 

 so far as Ave can find, that its pigment was red, it seems that Miss Lebour must 

 consider his var. nigrum (1887) as the equivalent of his polijphemus (1885), 

 although his figures of 1887 show black pigment, but no red. As shown else- 

 where by us (p. 000), we regard Pouchet's G. poJijpliemus (1885) and his G. 

 polypheimis vars. nigrum and roseum (1887) as three distinct species. The 

 uncertainty thus raised by jVIiss Lebour 's statement makes the allocation of her 

 record of occurrence to P. parva Lohmann somewhat tentative. 



Comparisons. — This is the smallest species known in the genus Pouchetin. 

 It is a member of the subgenus PouchcticUa with concentrated or smiple ocellus, 

 and, in so far as indicated by the structure of the ocellus, is nearest P. juno, 

 P. purpurata, P. rubescens, and P. violescens, though probably of simpler 

 organization than these species in other features. There appears to be no prob- 

 ability that it is near Protopsis nigra {Gymnodinium poli/pltrnnis var. nigrum 



