Fenestrate Bryozoans from the Glen Dean Limestone (Middle Chester) of Southern Indiana

Abstract

Fenestrate bryozoans are particularly abundant in shale and argillaceous limestone beds in the upper part of the Glen Dean Limestone (middle Chester) of late Mississippian age In south-central Indiana. Several hundred specimens were obtained from two excellent collecting localities in Perry County and from one exposure in northwestern Crawford County. The collected specimens are assigned to the genera Fenestella Lonsdale, Lyroporella Simpson, and Polypora McCoy of the Family Fenestellidae King and to the genus Septopora Prout, a member of the Family Acanthocladiidae Zittel. Fenesteila is the most abundantly represented genus in our collections and includes five species, Fenestella burlingtonensis Ulrich, F. cestriensis Ulrich, F. exigua Ulrich, F. matheri Condra & Elias, and F. tenax Ulrich. Polypora is the next most abundant genus and is represented in the fauna by three species, Polypora corticosa Ulrich, P. multispinosa McFarlan, and P. nodolinearis McFarlan. Frequency-distribution diagrams showing number of branches and fenestrules in a 10-millimeter distance and number of zooecia and nodes in a 5millimeter distance have been prepared for each described species except Septopora cestriensis Prout; only one specimen of this species displays the obverse side of the frond. Such diagrams permit clearer differentiation of closely allied species in which ranges of one or more structural characters may overlap, and these diagrams present a more accurate understanding of each species. The Glen Dean fenestrate bryozoan fauna, exclusive of Archimedes Owen, which is not treated in this study, includes 11 species. Although fenestrate bryozoan faunas have been described in considerable detail from Glen Dean beds in Illinois and Kentucky, these faunal elements of the Glen Dean of Indiana hitherto have not received significant attention.