scuta

The sack (in specimens long kept in spirits) is dirty purple, and exteriorly between the scuta, dark purple.

Valves smooth, thin, brittle; scuta with internal umbonal teeth on both sides.

Terga, large, nearly equalling the scuta in area, flat and sub-triangular; the scutal margin is not quite straight.

Scuta: these are striated longitudinally in close lines, generally plainly, but to a variable degree.