The Echinoid Directory

Key to the genera of Prenasteridae

1a. Frontal groove clearly developed.
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1b. Anterior of test flat to convex.

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2a. Apical disc with three gonopores.

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2b. Apical disc with four gonopores.

3a. Anterior and posterior petals subequal and obviously sunken

3b. Anterior petals much longer than posterior petals and both only slightly depressed.


4a. Apical disc subcentral or slightly posterior of centre; petals cruciform, the posterior less than half the length of the anterior.
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4b. Apical disc markedly anterior; anterior petals almost at 180 degrees and almost as long as the posterior petals.

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5a. Pores in the anterior column of the anterior petals are entirely rudimentary.


5b. Pores in the anterior column of the anterior petals are rudimentary only in the upper part.


6a. Lateroanal part of marginal fasciole absent. Aboral tubercles heterogeneous.


6b. Lateroanal part of the marginal fasciole present. Aboral tubercles fine and uniform.

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7a. Posterior strongly undercut; periproct very large.

7b. Posterior vertically truncate; periproct relatively small at top of truncate face