Growth series of immature crinoids of Synbathocrinus canandaigua (Goldring) and Cyttarocrinus eriensis (Hall) begin with simple armless calyxes in infancy and gradually develop arms during adolescence. Maturity is attained with the development of an anal structure and a complete tegumen. The sequence of arm development of S. canandaigua differs from known growth sequences of other crinoids, but is comparable to Kallimorphocrinus Weller, 1930. The growth sequence of C. eriensis is the same as that for Allagecrinus Carpenter and Etheridge, 1881, and indicates possible taxonomic relationship.

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