THE PERIDINIALES OF PLYMOUTH SOUND. 195 
(51) N.R. Spirodinium crassum (Pouchet) (Fig. 12). I have referred 
to this species a somewhat rare form which is definitely 
smaller than the type, length 0-075 mm. (type 0:12-0:2 mm. 
Fia. 11.—Spirodinium concentricum n. sp. 466. 
a large form, 6 small form. 
Pouchet). In shape and contour of the furrows it corresponds 
and has a diffuse colouring of brownish red beginning at the apex 
and following the transverse furrow. Faint longitudinal strize 
Fic. 12.—Spirodinium crassum (Pouchet). x 466. 
a ventral view, b dorsal view. 
are present ; transverse furrow with its ends widely separated, 
longitudinal furrow weakly developed. Nucleus posterior. 
Interior of body full of large granules. Occurs occasionally 
in June. 
