Chromatophores round, angular or irregular discs usually without pyrenoids (Karsten).
Rattray's classification is here followed, so far as it refers to our species.
Excentrici.—Valves circular; central space absent; markings angular, in oblique, decussating rows.
Lineati.—Central space absent; markings angular, oblique decussating rows straight.
Fasciculati.—Markings fasciculate, or sometimes only near the border.
Radiati.—Markings rounded or angular, more or less radiate.
Elaborati.—Valves elliptical, markings rounded.
EXCENTRICI
COSCINODISCUS EXCENTRICUS EHR.
Valve with a hyaline excentric space from which proceed, usually in six directions, rows of polygonal markings decreasing toward the narrow, coarsely striated border, the rows appearing convex toward the centre. Apiculi at unequal distances apart. Quite variable in size.