NOTES ON DINOFLAGELLATES. 23 



in great numbers, together with naviculoid diatoms, in late 

 summer of 1921. Also present, but less abundant, in late 

 summer of 1920 and early summer of 1922. Discolouration is 

 yellower than that caused by other dinoflagellates. Maximum 

 range from below lighthouse to a little south of St. Catherine's 

 Well in a band about 20 yards wide at the upper limit of 

 wet sand. (See Sketch Map 2). Most abundant at south 

 end of range. 



Description. Body nearly symmetrical, flattened 

 laterally, the greatest dorso ventral axis being about 1*7 of the 

 transverse axis and 0'75 of the total length. Epicone very 

 small and imperfectly divided from the hypocone. Girdle 

 asymmetrical, passing in an anterior direction slightly to the 

 left of the middle line. At the extreme apex the girdle crosses 

 the middle line and continues dorsally and now slightly to the 

 right. It gradually fades out, but the transverse flagellum 

 passes on round the body to the left side at a distance, 

 from the apex, of rather more than a quarter of the 

 total body length. Sulcus extending to within one trans- 

 diameter (measured from side to side) of the antapex and 

 partly overhung by the projecting left border. Longitudinal 

 flagellum hardly any longer than the body and often lying free 

 from the anterior end of the sulcus. Body enclosed in a 

 distinct homogeneous and colourless pellicle, from which, 

 under adverse conditions, the cytoplasm may be retracted. 

 Two highly refractile bodies, having the appearance of the 

 amyloid bodies of the Adiniferidea, occur one on each side. 

 Protoplasm of a uniform yellow ochre colour. Nucleus 

 posterior and slightly dorsal, elongated and often gently curved 

 to fit the contour of the body. Length about 70//. 



Amphidinium, herdmam, Kofoid. Principal cause of 

 discolouration during spring. In bulk causes greenish brown 

 patches, which always disappear before the in-coming tide and 

 do not reappear until that region of the beach is again exposed. 



