MORPHOLOGIC VARIATION WITHIN AND AMONG POPULATIONS OF THE CAMERATE CRINOID AGARICOCRINUS (LOWER MISSISSIPPIAN, KENTUCKY AND TENNESSEE) - BREAKING THE SPELL OF THE MUSHROOM

Morphologic variation within and among populations of the common monob athrid camerate crinoid Agaricocrinus was investigated using multivari ate and bivariate techniques for samples from 15 localities in the Low er Mississippian (late Osagean) Fort Payne Formation of south-central Kentucky and north-central Tennessee. Despite a wide range of variabil ity, two morphotypes were distinguished at most localities in both aut ochthonous and allochthonous carbonate facies: Agaricocrinus americanu s and the less common A. crassus. Morphologic characters that can be r eliably used to separate these taxa include character of the anal area , width of the second primibrachial, and shape of the arm facets. Many other characters of calyx shape and plate proportions used previously for species recognition, such as depth of the basal concavity, height of the interbrachials, height of the tegmen, and number of arms, are widely variable within populations. Variation within species populatio ns is ontogenetic, although a geographic component is recognized withi n A. crassus. The definition of A. crassus is emended to encompass a b roader range of variation than heretofore realized. Eight species prev iously reported from the Fort Payne Formation are placed in synonymy: A. arcula, A. dissimilis, A. elegans, A. podagricus, A. ponderosus, A. profundus, and A. tugurium are junior synonyms of A. americanus. A. a ttenuata is a junior synonym of A. crassus.