| It is by the position of the umbo in the grave that this fact has been exactly ascertained. |
| The paracentesis knife is inserted boldly through the membrane a little behind and above the umbo. |
| The cuticle is smoky olive to fuliginous, darker when young, becoming paler as the pileus expands, but always darker on the umbo. |
| The larva remains symmetrically shaped until about 240 µm, at which size the umbo extends above the hinge line and becomes more protuberant. |
| They are sometimes bell-shaped and then flattened, often with a mound or umbo. |
| The umbo forms at the point where the two valves meet and becomes protuberant early in the larva's development. |
