190 MARIE V. LEBOUR. 
(43) G. achromaticum n. sp. (Fig. 5). Related to G. viridis 
but without chromatophores. Perfectly colourless and trans- 
parent, transverse groove conspicuously left-handed, longitudinal 
groove reaching to the extreme posterior end. Apex somewhat 
excentric. Body covered with longitudinal striz. Nucleus 
posterior. One specimen only in July, 1915. 
(44) N.R. G. rhomboides Schiitt (Fig. 6). One of the commonest 
in this area appears to be the species figured by Schiitt (1895, 
Plate X XI, Figs. 63, 1 and 2) with the above name. Apparently 
no description of it exists except the short diagnosis in “ Nor- 
disches Plankton” (p. 99). Certain aspects of my specimens 
agree very closely with Schiitt’s figures, and I have therefore 
taken the name given by him rather than create a new one. 
Fic. 5.—Gymnodinium achromaticum n. sp. 466. 
a ventral view, b side view. N=nucleus. 
The species referred to by Dogiel (1906) as Gymnodinium spirale 
v. obtusum is from his figures certainly a true Gymnodinium and 
not a Spirodinium, to which now G. spirale and all its varieties 
have been transferred. The original figures by Bergh of G. spirale 
show it to be a Spirodinium with the ends of the transverse 
groove far apart, moreover Schiitt’s figure of v. obtusum shows 
also the same character. Dogiel’s species probably belongs to 
G. rhomboides or else some closely related form. His specimens, 
however, are very much larger than mine. His figures of the 
stages in division show it in another form which is also common 
with us and which I have found in division and very similar to 
Dogiel’s figures. Schiitt’s figure 63, 1 is also of this type, and 
apparently this is the form before and during division. These 
two forms I have therefore placed together as Gymnodinium 
rhomboides. The body is elongated, oval or rhomboidal, the 
transverse groove is only slightly displaced and_ left-handed, 
