The Echinoid Directory

 Micrasterine spatangoids with:

• ethmolytic apical disc with genital plate 2 extending behind the posterior ocular plates
• labral plate short and wide, not in contact with ambulacral plate 2
• episternal plates tapering posteriorly
• petals narrow and parallel-sided, without wide perradial zone; generally sunken
• peripetalous and subanal fascioles present.

Eocene to Recent; worldwide.

Distinguished from other Micrasterina by the short and wide labral plate that does not extend beyond the first ambulacral plate and by its relatively narrow and parallel-sided petals.

The following taxon is most probably a brissid but is not included in the key:
Idiobryssus