KOFOID AND SWEZY: UNARMORED DINOFLAGELLATA 151 



length of the epieone is about 0.16 of tlie total length, measured from the proximal end of the 

 girdle ; its transdiameter, measured on the anterior lip of the girdle, is about 0.6 the greatest trans- 

 diameter of the hypocone, and its doi-soventral diameter about 0.33 of the same. The apex is 

 flattened and slopes to the right at an angle of 15° to 17° from the horizontal. It is traversed 

 by the sulcus, which crasses the apex and swings around to the left, encircling a small terminal 

 button, somewhat as in some species of Pouch etia. Tlie hypocone is broadly ellip.soidal, its greatest 

 length, on its left shoulder, about 1.5 its greatest diameter, which is located about mid- 

 way between girdle and antapex. Dorsoventrally it is widest at 0.33 of its length from the 

 antapex, expanding gradually from the girdle, where its dorsoventral diameter is 0.66 of the 

 diameter at its widest part, and contracting at the antapex to an almost hemispherical outline in 

 lateral view, broken, however, by the deep semicircular notch at the posterior end of the sulcus. 

 This notch is about three times the width and depth of the girdle. It lies a little to the right of 

 the main axis and the left margin is the larger and longer one. 



The girdle forms a descending left spiral, deepest at its ends, both of which are sharply 

 deflected posteriorly at angles of 30° and 45° respectively at the proximal and distal regions. 

 The distal displacement posteriorly is about twice the width of the girdle. There is no over- 

 hang. Tlie furrow is deeply impressed with broadly rounded lips. The transverse flagellum 

 completely encircles the body. 



The sulcus runs the whole length of the body, tej-minates anteriorly in a sinistral loop around 

 an apical button, has a slight sigmoid curve at the girdle and flares posteriorly in the antapical 

 notch. A ventral lobe on the right side at the posterior end pushes it somewhat to the left. The 

 longitudinal flagellum extends from the flagellar pore near the posterior end of the sulcus 

 posteriorly beyond the antapex for a distance equal to the length of the bodj'. 



The surface is minutely and faintly striate with equidistant, parallel, longitudinal lines, about 

 eighteen across the dorsal face. They show faintly on the epieone, but more clearly on the 

 hypocone. 



The cell contents consist of the posteriorly located ellipsoidal nucleus and numerous peripheral 

 greenish spherules of high refractive index, probably fatty products of metabolism. No definite 

 chromatophores could be detected. The whole body has a pale, sea foam gi-een tone, due in part 

 at least to the refractive bodies. All inclusions in the form of yellowish spheres, red, and orange 

 spherules in different individuals are indications of the holozoic nutrition of this organism. 



Luminescence not observed. 



Dimensions. — Length of body, 56/^; transdiameter in girdle, 20m; at widest 

 part, 32m; dorsoventral, 18m. 



Occurrence. — Taken frequently in washings from ])eaeh sand on ocean shore 

 at La Jolla, California, in July, 1914. 



Comparisons. — This species is referred to Amphidininm rather than Gymno- 

 dinium because of its reduced epieone, deeply incised sulcus, and dorsoA^entral 

 compression. The large size of the epieone allies it with Gumnndinium, but 

 this feature is shared with Amphidinium asijmmctricutH, A. sulcdtum, A. corpu- 

 lent um and to some extent with A. tmncatmn (figs. U, 5, 10, 6, 3). The extension 

 of the sulcus upon the epieone is also a feature of A. corpulentum and A. sul- 

 catum. Linear striae have been recorded in Ampliidinium only on this species 

 and A. asijmmctricum and .1. truncatum. 



