An apical pore field may be visible on one or both ends of the valve. These genera have raphes on both valves, raised above the valve surface on a structure called a keel. The keel may be on the midline of the valve or displaced toward the valve margin. In these genera, valve surface ornamentation is radially symmetric around a central point, but the valve outline is bipolar or multipolar. These genera also have a raphe on both valves, but it is reduced to a short structure on each end of the valve.
Longitudinal axis is usually bent.
The convex margin of some species is elaborately scalloped. These genera have a raphe on both valves and are symmetrical to both the longitudinal and transverse axis of the valve. This is a very large and diverse group. These genera have a raphe on both valves which is borne on a specialized tube-like structure called a canal. The canal raphe is usually displaced from the midline of the valve.