AMPHORACRINIDAE IN NORTH AMERICA (CRINOIDEA, ECHINODERMATA)

The Amphoracrinidae was an important crinoid family in Western Europe during the Mississippian, and Amphoracrinus was the dominant genus. Recognition of Amphoracrinus in North America has been problematic for more than 150 years, during which time many lower Mississippian camerate crinoids with a high tegmen or with spinose tegmen plates were assigned incorrectly to Amphoracrinus.

Here, the family Amphoracrinidae is redefined, six genera are recgonized in this family. Each genus is uniquely diagnosed with the following genus-level characters: calyx shape, calyx lobation, relative height of basal circlet, visibility of basal circlet in lateral view, shape of first primibrachial, number of fixed secundibrachials, whether secundibrachials are present in arm lobes, number of fixed tertibrachials, proximal plating in the posterior interray, tegmen height relative to calyx height, tegmen shape, shape and spinosity of the distal tegmen, character of oral plates, shape of oral plates, position of anal tube, orientation of anal tube, distal tegmen spinosity, orientation of proximal free arms, and branching or lack of branching in the free arms.

Globally, this family occurred from the Ivorian (Tournaisian;Tn3a-Tn3c) through the Brigantian (Visean; V3c) . Amphoracrinus is relatively rare in North America, but it occurs in the Cuyahoga Formation (late Kinderhookian) of Ohio and the Anchor Limestone (late Kinderhookian to early Osagean) of Nevada. Other North American Amphoracrinidae are Ancalocrinus, Dilatocrinus, and Displodocrinus, which occur in the late Kinderhhookian through the middle Osagean.