The Echinoid Directory

Key to the genera of Polycidaridae

1a. Ambulacral tuberculation heterogeneous throughout.
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1b. Ambulacral tuberculation simple at ambitus and adapically; heterogeneous only adorally.

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2a. Pore-pairs non-conjugate; interporal partition no larger than a single pore diameter and not raised. Primary spines long and slender and ornamented with scattered coarse thorns.


2b. Pore-pairs subconjugate; the two pores separated by a relatively wide, raised node.

Paracidaris (Go to 3)

3a. Primary tubercles non-crenulate.

Paracidaris (Alpicidaris)

3b. Primary tubercles crenulate.

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4a. Primary spines relatively short and ornamented with dense rows of blunt thorns.

Paracidaris (Paracidaris)

4b. Primary spines long and slender and ornamented with rows of fine thorns.

Paracidaris (Anisocidaris)

5a. Scrobicular tubercles forming a raised ring; interradial and interradial zones rather sparsely tuberculate.


5b. Scrobicular tubercles not elevated or differentiated; interradial zone comparatively densely tuberculate.