File:Conodonts from the Glen Dean formation (Chester) of the Illinois basin (1958) (20492824740).jpg

Title: Conodonts from the Glen Dean formation (Chester) of the Illinois basin
Identifier: conodontsfromgle209rexr (find matches)
Year: 1958 (1950s)
Authors: Rexroad, Carl Buckner, 1925-
Subjects: Conodonts; Paleontology; Paleontology
Publisher: Urbana
Contributing Library: University of Illinois Urbana-Champaign
Digitizing Sponsor: University of Illinois Urbana-Champaign

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20 ILLINOIS STATE GEOLOGICAL SURVEY
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Fig. 14.—Diagrammatic reconstruction of a mature representative of Lambdagnathus Rexroad, n. gen., showing outer lateral (A), aboral (B) and outer posterior (C) views, X35. also is inclined sharply downward. Typi- cally, it is arched, slightly bowed convexly anteriorly, is deepest near its midlength, and has denticles largest near its midsection and decreasing in size in either direction, the larger denticles being considerably larger than the apical denticles. Attach- ment scars may be prominent on the faces of the inner lateral process, less so on the posterior bar and anterior process. Chief variations in the genus are expected to be in the proportions of the lengths of the three processes and their angular relations to each other, plus variations in the dentic- ulation and depths of the processes, partic- ularly the inner lateral one. Relationships of this genus to other gen- era are problematical. The general form is most similar to that of Centrognathodus Branson and Mehl, but it differs particu- larly in the angular relations of the three processes, in the presence of a pronounced triangular subapical pit in Lambdagnathus, and in its triangular apical denticle. Lambdagnathus fragilidens Rexroad, n.sp. Plate 6, figures 10-16 New Genus ? (Part), Rexroad, 1957, Illinois Geol. Survey Rept. Inv. 199, p. 41, pi. 4, fig. 10 only. Posterior bar delicate, no thicker than the four posteriorly inclined laterally com- pressed denticles it typically bears. Ante- rior process curves outward at juncture of bars, then continues direction of posterior bar. Anterior process thin, of uniform depth, with about twelve denticles which are slightly smaller toward anterior end of process. Inner lateral process viewed orally appears nearly perpendicular to posterior bar, viewed anteriorly is inclined down- ward approximately 45°. Inner lateral process deepest about one-third distance from juncture of processes, with two largest denticles located here, denticles strongly compressed in plane of process, slightly re- curved, and typically number from nine to eleven. Apical denticle larger than den- ticles of posterior bar, triangular in shape with sharp edge in line with each process, slightly recurved. Well defined triangular pit beneath apical denticle with grooves extending from it along the thin aboral margin of each of the processes. Material studied.—19 specimens. Distribution.—Glen Dean Formation of Illinois, Indiana, and Kentucky.

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