(2) Polymyxus.—Sectors convex.
Actinoptychus Ehr. (1839) em. V. H. (1890)
(actis, a ray, and ptyx, a fold)
Frustule cylindrical, less in length than the diameter, in zone view undulated. Valve divided into six or more sectors alternately raised and depressed, areolate and punctate, varying in the alternate divisions. The areolation is confined to the outer layer of the valve while the punctation is usually on an inner valve often found detached. Processes on the border, three or more. Umbilicus circular or angular, hyaline.
ANALYSIS OF SPECIES
| Sectors, six | undulatus |
| Sectors, eight or more, cellular | heliopelta |
| Sectors, fourteen, punctate | vulgaris |
ACTINOPTYCHUS UNDULATUS (KUETZ.) RALFS
Valve areolate and punctate in quincunx, divided into six equal sectors, alternately elevated or depressed, their areolations appearing different. Margin well defined. Umbilicus smooth, hexagonal. Processes three, sometimes six, inserted within the margin of each alternate division. Very variable in size and appearance.
This is the Actinocyclus of Bailey, figured and described in Amer. Jour. Science, 1842, p. 93, Pl. 2, Fig. 11, but not named. Kuetzing describes and names it and refers to Bailey.
Actinoptychus omphalopelta Ehr.