. Bulletins of American paleontology. 24 Bulletin 336 hore with about 11 segments; styloid robust, some spe- cies with extended rounded flanges; distal aulacophore with from 20 to more than 40 segments, and proximal segments markedly spinose. Occurrence. —Middle Ordovician: Trentonian of Tennessee and Kentucky. Late Ordovician: Edenian of Tennessee; Cincinnatian of Ohio, Kentucky, and Indiana. Discussion. —Caster's (1952) extensive paper on this genus eliminates the need for detailed description of the thecal plating (see Text-fig. 10). However, since that work, new aspects of the morphology h
. Bulletins of American paleontology. 24 Bulletin 336 hore with about 11 segments; styloid robust, some spe- cies with extended rounded flanges; distal aulacophore with from 20 to more than 40 segments, and proximal segments markedly spinose. Occurrence. —Middle Ordovician: Trentonian of Tennessee and Kentucky. Late Ordovician: Edenian of Tennessee; Cincinnatian of Ohio, Kentucky, and Indiana. Discussion. —Caster's (1952) extensive paper on this genus eliminates the need for detailed description of the thecal plating (see Text-fig. 10). However, since that work, new aspects of the morphology have become known. I will concentrate on these new findings in the M'2 U'3 U'4 CM'1. Text-figure 10.—Carapace (A) and plastron (B) o(Enoploura po- pei. This figure is based on UCM 25993 (PI. 6, figs. 1, 3). On the aulacophore; pa = proximal aulacophore; s = styloid. Forexplanationsofother plate abbreviations, see Table I (foldout inside back cover). Text-figure 11. —Articulating spines and articulating surface on M4/M'5 of Enoploura popei. Scale bar in all figures is 1 mm long. A, B, adsagittal (inside) side of a right spine. Note the articulating socket which abuts the mamelon and the bounding arcuate muscle ridge (Text-fig. 1 IF); C. D, absagittal views of a left spine, showing muscle ridge and pit. Presumably these pits were for attachment of muscles antagonistic to those on the opposite lateral surface. Muscles attached on this side would pull the spine laterally outward; those on the opposite surface would pull the spines laterally toward the sagittal plane; E, top view of a spine. The thickened end is the top side of the articulating area. Note how it would cover much of the articulating area; F, articulating area on an M4 plate. The raised boss IS the mamelon. The spine would articulate between the ma- melon and the left margin of the slightly-depressed articulating area (as viewed). All photos were taken on an Amray 1700 at a power setting of 30 kv. For ex
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