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Silurian Encrinurinae (Trilobita) from the Central United States

Kenneth C. Gass, Gregory D. Edgecombe, Lars Ramsköld, Donald G. Mikulic and Rodney Watkins
Journal of Paleontology
Vol. 66, No. 1 (Jan., 1992), pp. 75-89
Published by: Paleontological Society
Stable URL: http://www.jstor.org/stable/1305890
Page Count: 15
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Silurian Encrinurinae (Trilobita) from the Central United States
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Abstract

Silurian (Llandovery--Ludlow) Encrinurinae from Wisconsin, Indiana, and Illinois include species of Balizoma Holloway, 1980, Curriella Lamont, 1978, Distyrax Lane, 1988, Encrinurus Emmrich, 1844, Mackenziurus Edgecombe and Chatterton, 1990a, and Nucleurus Ramsköld, 1986. Mackenziurus lauriae n. sp. is described from Wenlock strata of the Racine and Sugar Run Dolomites; nine segments in the holaspid thorax are the fewest known for any encrinurid. A square rostral plate is diagnostic of Mackenziurus. New morphological data are provided by Illinois specimens of Balizoma indianensis (Kindle and Breger, 1904) from the Wenlock--Ludlow Racine Dolomite, and of Curriella tuberculifrons (Weller, 1907) from the Llandovery Elwood--Wilhelmi Formations. Nucleurus n. sp. is possibly from Llandovery strata in Wisconsin. Distyrax n. sp. occurs in the Brandon Bridge Member (late Llandovery--early Wenlock) of the Joliet Dolomite in Illinois. The type pygidia and possible topotype material of Encrinurus nereus Hall, 1867, confirm assignment to that genus as currently viewed; this reefal species is distinct from the closely related inter-reef species E. egani Miller, 1880, and appears to be distinct from reefal E. reflexus Raymond, 1916. Lectotypes are selected for these Encrinurus species.

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