. Early Llandovery crinoids and stelleroids from the Cataract Group (Lower Silurian) in southern Ontario, Canada . nus, Cyphocrinus, Dimerocrinites, Eudimerocrinus, and Griphocrinus. Macarocrinus, Pterinocrinus, and Pt\c ho- crinus are dimerocrinitids characterized by uniserial arms. Macarocrinus has large, differentiated orals, in contrast to the incompetent tegmen of Nexocrinus gen. nov., and has a different arm structure. The arms of Pterinocrinus possess compound bipinnulated brachials in contrast to the simple, uniserial brachitaxis of Nexocrinus. Similarity with Prychocrinus is much clos
. Early Llandovery crinoids and stelleroids from the Cataract Group (Lower Silurian) in southern Ontario, Canada . nus, Cyphocrinus, Dimerocrinites, Eudimerocrinus, and Griphocrinus. Macarocrinus, Pterinocrinus, and Pt\c ho- crinus are dimerocrinitids characterized by uniserial arms. Macarocrinus has large, differentiated orals, in contrast to the incompetent tegmen of Nexocrinus gen. nov., and has a different arm structure. The arms of Pterinocrinus possess compound bipinnulated brachials in contrast to the simple, uniserial brachitaxis of Nexocrinus. Similarity with Prychocrinus is much closer. Of the species at present assigned to Ptychocrinus, P. parvus (Hall), a species that should probably be removed from Ptychocrinus (see p. 20 for discussion), is allied most closely with A^. delicatulus. P. parvus resembles Nexocrinus in that it possesses concealed infrabasals, narrow, median ray ridges, and 20 uniserial, unbranched arms. P. parvus, however, has two fixed secundibrachials, while Nexocrinus possesses four. The CD-interray of Nexocrinus is wider than that of P. parvus and has a distinct anal ridge. The primanal of the specimen off. parvus figured by Hall (1872, pi. 5, fig. 17) supports a single series of three plates up to the level of the first axillaries, while the primanal of Nexocrinus supports an anitaxis that is flanked by smaller plates. Nexocrinus appears to be monotypic, but a thorough study of the Dimerocrinitidae is needed to determine whether or not additional species of the genus Nexocrinus exist. Text-fig. 8 delicatulus gen. et sp. nov. Holotype centred on DE-interray, ROM 666cl-A, PI. 3, fig. 4. Radials black; primanal wrinkle stipple; anals and interhrachials dot stipple. Scale 5 mm. Nexocrinus delicatulus sp. nov. Text-fig. 8; PI. 3, figs. 2-5 TYPE MATERIAL Only four specimens were sufficiently well preserved for study: holotype ROM 666cl-A; paratypes figured ROM 666cl-B, 39050, 39051. OCCURRENCE Whirlpool Formation at Cataract and
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