| The shell is ventricose, is closed or gapes slightly posteriorly, and has prominent subcentral umbones and an external ligament. |
| A bivalve is said to be oblique when it slants off from the umbones. |
| Below the umbones, the shell margin is folded inward forming a deep lunula and gaping between both valves. |
| The two valves are roughly triangular or bluntly oblong with rounded umbones near the anterior end. |
| Species on this family can be identified by its mytiliform form, sometimes quadrate, with the hinge edentulous and the umbos anterior or terminal. |
