Tarphophragma macrostoma (Loeblich, 1942)

(Figs 10 E-G; 11A; Appendix 1)

Hallopora macrostoma Loeblich, 1942: 430, pl. 62, figs 12-14.

Tarphophragma macrostoma – Key 1991: 207-209, figs 6.1-6.6.

MATERIAL EXAMINED. — CEGH-UNC 27520 c, d, CEGH-UNC 27539 c, d, g, CEGH-UNC 27537 d, CEGH-UNC 27538 d.

OCCURRENCE. — Bromide Formation, Upper Ordovician, lower Sandbian; Oklahoma, United States. La Pola Formation, Upper Ordovician, Sandbian; La Pola creek section near Albardon village, San Juan Province, Argentine Precordillera, western Argentina.

DESCRIPTION

Ramose colonies, branch diameter 3.0- 3.6 mm. Exozone distinct, 0.5-0.6 mm wide, endozone 2.0- 2.4 mm wide. Autozooecia long, growing parallel to branch axis for a long distance in endozone and bending sharply in exozone, having rounded-polygonal shape in transverse section in endozone. Autozooecial apertures oval to polygonal. Autozooecial diaphragms thin, planar, widely spaced in endozone; common to abundant in exozone, planar, rarely inclined, developed as extension of wall cortex. Mesozooecia arising in endozone, polygonal in transverse section, 2-6 surrounding each autozooecial aperture. Mesozooecial diaphragms planar, densely spaced. Acanthostyles absent. Autozooecial walls indistinctly laminated, 0.005 -0.008 mm thick in endozone; displaying distinct reverse V-shaped structure with dark autozooecial boundary, with weakly developed wall cortex continued in diaphragms, 0.04-0.12 mm thick in exozone. Maculae indistinct, consisting of macrozooecia.

COMPARISON

Tarphophragma macrostoma (Loeblich, 1942) differs from T. ovata (McKinney, 1971) from the Middle Ordovician of United States in larger autozooecial apertures (average aperture width 0.21 mm vs 0.17 mm in T. ovata; measurements for T. ovata from McKinney 1971), as well as in less abundant and smaller mesozooecia. Tarphophragma macrostoma differs from T. multitabulata (Ulrich, 1886) from the Middle Ordovician of United States in larger autozooecial apertures (average aperture width 0.21 mm vs 0.19 mm in T. multitabulata; measurements for T. multitabulata from Karklins 1984).