The Echinoid Directory

Key to the genera of Collyritidae

1a. Phyllodes extremely well developed with pore-pairs forming broad bands three pore-pairs wide, and with occluded plates.

1b. Phyllodes weakly developed with just 4-6 pores in each column larger close to the mouth.

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2a. Periproct supramarginal on sloping posterior face; test elongate and peristome subcentral.


2b. Periproct marginal to inframarginal; test not elongate.

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3a. Frontal groove well developed; peristome close to anterior border and facing forwards into anterior groove.
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3b. Frontal groove poorly developed or absent; peristome downward-facing at some distance from the anterior border.

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4a. Pore-pairs in anterior ambulacrum differentiated from those in paired ambulacra; paired ambulacra with well-developed circumflexed pore-pairs.

4b. Pore-pairs in all five ambulacra similar; small and obliquely orientated.

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5a. Apical disc with only small scattered catinal plates between anterior and posterior parts. Test tapering to blunt point at posterior.
5b. Apical disc with a continuous series of catinal plates running between anterior and posterior parts. Test not tapering posteriorly.
6a. Periproct marginally; aboral ambulacral pores microscopic.
6b. Periproct aboral, in groove; aboral ambulacral pores clearly visible.