KOFOID AND SWEZY: UNARMORED DINOPLAGELLATA 199 



descending left spiral. Tlie first part of its course makes a short, abrupt posterior turn, beyond 

 which it turns anteriorly until it reaches the dorsal side. It passes across this in a nearly 

 transverse direction, turning posteriorly on the ventral face, joining the sulcus with a posterior 

 displacement of 0.2 transdiameter. The furrow is wide, about 0.06 transdiameter, and deeply 

 impressed. The sulcus extends in a sinuous line from tlie left side of the apex to the antapex. 

 On the hypocone it lies at the base of a deep trougli which indents the ventral face. The sides 

 become widely deflected near the antapex. The anterior flagellar pore evidently opens at the 

 proximal junction of the girdle and sulcus, the posterior pore near the distal junction. 



The nucleus is a large, ellipsoidal body in the anterocentral part of the hypocone. Its major 

 and minor axes are 0.73 and 0.6 transdiameter respectively. The remainder of the cytoplasm 

 is filled with numerous, greenish yellow chromatopliores. 



DIMENSIONS. — Length, 60/* ; transdiameter, 32^ ; axes of nncleus, 32/* and 19/*. 



Occurrence. — This species was figiu-ed hy Lebour (19175) from a single 

 specimen taken in June from the waters of Plymouth Sound, England. 



Comparisons.^ — This form is evidently one of the connecting links between 

 Ampliidimnm and Gi/»i)iodinium, as shown in its structure. The epicone, how- 

 ever, has a relative length too great to include it with Aniphidinium. This form 

 and the one described by Lebour (1917?0 as Gymnodinium pseudonoctUuca are 

 separated mainly by size and a slight variation in color. It belongs in the sub- 

 genus Gym nodinium . 



Synonymy. — The name, G. viridift, assigned to this species by Miss Lebour 

 (]917?>), is preoccupied by Penard's (1891) species, G. viride. We therefore 

 propose for Lebour 's species the name G. conicum. 



Gymnodinium contractum sp. nov. 



Plate 5, figure 52 ; text figure X, 2 



Diagnosis. — A small species with subovoidal l)ody, its length 1.43 transdi- 

 ameters; girdle submediau, without displacement; sulcus on h^q:)oeone only; 

 surface on epicone furrowed; plasma green with rose red granules. Length, 

 63/*. Pacific off La Jolla, California, August. 



Description. — The body is subovoidal, with broad apices, nearly circular in cross-section, 

 widest anteriorly, its length 1.43 transdiameters at tlic widest part. The epicone exceeds the 

 hypocone in size, its lengtli being greater by about 0.14 of itself, and its transdiameter somewhat 

 greater. The epicone is subhemispherical in outline with the apex protruding slightly be.yond 

 the broad curve of the anterior part of the body. Its length is 0.52 of the total length of tlie 

 body. The hypocone is somewhat narrower than the epicone, sliarply contracted a short distance 

 below the girdle to 0.77 transdiameter of the epicone. It expands slightly posteriorly, where 

 it is rounded with deeply notched antapex. 



The girdle is sulimedian in position, its distance from the apex al)out 0.52 of the total length 

 of the body. The furrow is wide, about O.OS ti-ansdiametei' in width, and deeply impressed with 

 smooth, overhanging bordeJ-s. It foi-ms a coinjilete circle around tlu' body without displacement. 

 Tile sulcus extends from the girdle posteriorly to the aiitajiex. It forms a shallow channel 

 anteriorly and about midway of its length widens ami a1 tli(> same time sinks deeply into the 

 body, deeply excavating the ventral surface of the antai)ex. Tlie anterior flagellar pore opens 

 at the junction of girdle and sulcus, the posterior pore aliout two widths of the girdle posterior 

 to that point. 



